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Journal of the 

Society of Motion Picture Engineers 

VOLUME 51 JULY 1948 NUMBER 1 



PAGE 

Brightness and Illumination Requirements H. L. LOGAN 1 

Light Modulation by P-Type Crystals . GEORGE D. GOTSCHALL 13 

Portable 16-Mm Sound Projector H. H. WILSON 21 

Optical Problems in Large-Screen Television. . . .1. G. MALOFF 30 

Developments in Large-Screen Television . RALPH V. LITTLE, JR. 37 

Discussion Large-Screen Television 47 

Motion Picture Theater Air Conditioning . D WIGHT D. KIMBALL 52 

Air Purification by Glycol Vapor J. W. SPISELMAN 70 

Ultraviolet Air Disinfection in the Theater. . .L. J. BUTTOLPH 79 

Service and Maintenance of Air-Conditioning Systems 

W. B. COTT. 92 

Discussion Ventilating and Air Conditioning 94 

Display Frames in the Motion Picture Theater. .LESTER RING 101 

Society Announcements 104 

Book Review: 

"Developing Technique of the Negative," by C. I. Jacobson 

Reviewed by Joseph S. Friedman 105 

Current Literature . . 106 



ARTHUR C. DOWNES HELEN M. STOTE GORDON A. CHAMBERS 

Chairman Editor Chairman 

Board of Editors Papers Committee 



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342 Madison Ave., New York 17, N. Y. Entered as second-class matter January 15, 1930 
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Copyright, 1948, by the Society of Motion Picture Engineers, Inc. Permission to republish 
material from the JOUBNAL must be obtained in writing from the General Office of the Society. 
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Society of 

Motion Picture Engineers 

342 MADISON AVENUE NEW YORK 17, N. Y. TEL. Mu 2-2185 
BOYCE NEMEC . . . EXECUTIVE SECRETARY 

OFFICERS 

1947-1948 

PRESIDENT EDITORIAL VICE-PRESIDENT 
Loren L. Ryder Clyde R. Keith 

5451 Marathon St. 233 Broadway 

Hollywood 38, Calif. New York 7, N. Y. 

PAST-PRESIDENT CONVENTION VICE-PRESIDENT 
Donald E. Hyndman William C. Kunzmann 

342 Madison Ave. Box 6087 

New York 17, N. Y. Cleveland, Ohio 

EXECUTIVE VICE-PRESIDENT SECRETARY 
Earl I. Sponable G. T. Lorance 

460 West 54th St. 63 Bedford Rd. 

New York 19, N. Y. Pleasantville, N. Y. . 

1948-1949 

ENGINEERING VICE-PRESIDENT FINANCIAL VICE-PRESIDENT 

John A. Maurer James Frank, Jr. 

37-01 31st St. 18 Cameron PI. 

.Long Island City 1, N. Y. New Rochelle, N. Y. 

TREASURER 

Ralph B. Austrian 
247 Park Ave. 
New York 17, N. Y. 

Governors 

1947-1948 

John W. Boyle Robert M. Corbin Charles R. Daily 

1207 N. Mansfield Ave. 343 State St. 5451 Marathon St. 

Hollywood 38, Calif. Rochester 4, N. Y. Hollywood 38, Calif. 

David B. Joy Hollis W. Moyse 

30 E. 42d St. 6656 Santa Monica Blvd. 

New York 17, N. Y. Hollywood, Calif. 

1948 

William H. Rivers S. P. Solow R. T. Van Niman 

342 Madison Ave. 959 Seward St. 4431 W. Lake St. 

New York 17, N. Y. Hollywood, Calif. Chicago, 111. 

1948-1949 

Alan W. Cook Gordon E. Sawyer 

4 Druid PI. Lloyd T. Goldsmith 857 N. Martel St. 

Binghampton, N. Y. Burbank, Calif. Hollywood, Calif. 

Paul J. Larsen 

Los Alamos Laboratory 
University of California 
Albuquerque, N. M. 



Brightness and Illumination 
Requirements* 

BY H. L. LOGAN 

HOLOPHANE COMPANY, INC., NEW YORK 17, NEW YORK 



Summary This paper analyzes the problem presented by the con- 
tinuous lighting of motion picture theater auditoriums; gives data on screen 
brightness with various types of film running; relates auditorium brightness 
to average screen brightness with film running; proposes a specific arrange- 
ment of brightnesses from screen background to theater lobby; and suggests 
a practical method by which this arrangement of brightnesses may be 
attained with standard lighting equipment. 



THE CONTINUOUS LIGHTING of motion picture theaters is a rather- 
special problem. The tentative and controversial rules sug- 
gested in Report No. 1 on l 'Brightness and Brightness Ratios" of the 
Illuminating Engineering Society do not seem to apply, as they are 
for spaces in which critical seeing tasks occur, and in which the object 
of regard is a detail seen at close range. 

The screen is the object of regard in a motion picture theater and is 
seen at an average minimum distance 1 of 22.5 feet. This distance is 
greater than the minimum at which the ciliary muscles tense in order 
to bring an object into focus. 2 That is, the observers' lenses are in a 
relaxed state at all screen-viewing distances in the average motion 
picture theater, which is characteristic of distant, rather than close- 
range vision. 

The three-to-one rule 3 would be impossible to apply in any event as 
diffusion from the interior of the house would put an overlay of light 
on the screen that would greatly reduce contrasts. Mimimum screen 
brightnesses, with film running, as measured by the writer (see Table 
I), ran as low as l /w of the average brightness. Still lower bright- 
nesses were frequently encountered but they were below the range of 
the instrument used and could not be accurately measured. The 
author estimates that minimum brightnesses of 1 /w of the average 
brightness are common. 

* Presented April 21, 1948, at the Atlantic Coast Section in New York. 

JULY, 1948 JOURNAL OF THE SMPE VOLUME 51 1 



2 LOGAN July 

If the interior of the house was lighted to a brightness of one third 
the average screen brightness (with film running) , and in such a way 
that no direct light could reach the screen, the screen could still re- 
ceive an overlay of light by diffusion from the house surfaces that 
would approach one third of the average screen brightness. In this 
case details that had a brightness less one third of the average screen 
brightness would tend to be washed out, and brighter contrasts would 
be diluted. 

TABLE I 

MEAN BRIGHTNESS MEASUREMENTS OF MOVING PICTURE SCREENS 

Brightness In Foot-Lamberts 
Screen - With Film Running 
Film Blank Minimum Average Maximum 



Black-and-white news 


15.0 


0.35 


1.08 


2.50 


Black-and-white feature 


15.0 


0.04 


1.09 


5.10 


Black-and-white news 


13.6 


0.26 


1.42 


4.20 


Cine-color short 


15.0 


0.53 


1.40 


2.70 


Technicolor feature 


10.1 


0.18 


1.27 


5.63 


Technicolor travelog 


15.0 


1.20 


2.40 


3.70 


Self-colored animated cartoon 


10.1 


0.36 


1.65 


4.73 


Self-colored animated cartoon 


15.0 


0.53 


2.80 


5.90 



Such washing out and dilution of screen detail would not be accept- 
able and so the subject must be approached from another angle. It 
is for this reason that the author undertook to measure screen bright- 
nesses with film running. Until such brightnesses were known, engi- 
neers would be guessing at permissible brightnesses in the rest of the 
observer's field of view, as such brightnesses obviously had to be con- 
siderably less than screen brightnesses in order not to wash out 
screen detail with an overlay of diffused light originating from the 
walls, ceiling, and floor of the illuminated auditorium. 

Measurements of screen brightnesses with film running were not 
possible until the development of the instrument shown in Fig. 1. 
This instrument has a specially shaped mirror that picks up the same 
field of view as an observer. The mirror is viewed by a photosensi- 
tive electronic cell and the results read on a milliammeter. When the 
instrument is so located with respect to the screen that the screen sen- 
sibly fills the fteld of the instrument, and no other light approaches 
from any other part of the instrument field, the needle deviation is a 
measure of the total light coming from the screen at any instant. The 



1948 



BRIGHTNESS AND ILLUMINATION REQUIREMENTS 



instrument is equipped with filters to correct the response ol the elec- 
tronic cell to that of the standard observer, the action of the 
instrument being independent of human judgment, and automatic. 

The instrument measures "steradian foot-lamberts," which can be 
converted into other units when the distance of the instrument from 
the source of light is known, or when there is some reference condition 
to tie to, such as the brightness of the blank screen (which was sepa- 




Fig. 1 Logan fluxmeter. 

rately measured by two observers with two different Luckiesh-Taylor 
Brightness Meters in this investigation). 

The writer has adopted the average screen brightness with film 
running as the basic reference criterion in the design of motion picture 
theater lighting. Previous investigators, having no way of arriving at 
instantaneous average brightness for entire screen with film running, 
have used stills and measured the "white" and the "blacks" which 
they have then used as reference values. 4 - 5 The eye may spend as 



LOGAN 



July 



BLACK AND WHITE "NEWS" 



BLACK AND WHITE FEATURE "LURED" 




TIME 



NORMANDIE THEATRE N.YC 
MIN BRIGHTNESS 0.04 FT-L 




\AVER. 1.09 
MAX. 5.10 






, 




H 




ft 


UH 


r^~ 


Jl/ V 


^ \/\i 



TIME 



BLACK AND WHITE "NEWS" 



SELF-COLORED ANIMATED CARTOON 



PARK AVE. THEATRE N.YC. 
MIN BRIGHTNESS 0.26 FT-L. 
AVER. " 
MAX. 4.20 




TIME 



NORMANDIE THEATRE N.YC. /\ 
MIN. BRIGHTNESS 0.53 FT-L/ \ 




TIME 



CINE COLOR "SHORT" 



NORMANDIE THEATRE N.YC. 
MIN BRIGHTNESS 0.53 FT-L 
AVER. 1.40 * 

MAX 2.70 




TIME 



SELF-COUORED ANIMATED CARTOON 



PARK AVE. THEATRE N.YC. 
MIN BRIGHTNESS 0.36 FT^L 
AVER. n " 1.65 

MAX. In 4.73 




TIME 



TECHNICOLOR "TRAVELOG" 



NORMANDIE THEATRE N.YC. 
MIN BRIGHTNESS 1.20 FT-L 




AVER. Z40 
MAX. 3.70 




C\^ 


M \l^ 


\ 


^^ 




TIME 



FIG. 2 Sequence of brightness changes for various types of film. 



1948 



BRIGHTNESS AND ILLUMINATION REQUIREMENTS 



S3 






sil 



^> 



little as 5 /ioo second on a fixation point, and its fixation pauses nor- 
mally average 15 /ioo second. 6 Motion picture film is moved along at a 
rate that is based on this fact and its complement, the persistence of 
vision. As a result the eyes in screen viewing seldom have an oppor- 
tunity to rest on a fixation point long enough to adapt to it. The 
author believes that with the rapidly fluctuating brightness of the 
screen with picture running, the eyes have no choice but to adapt to 
the mean screen brightness. See Fig. 
2 for sequence of brightness varia- 
tions on screen as a whole, for films 
measured. 

If we adopt the lowest mean bright- 
ness, as measured in this investigation, 
that is likely to be met. namely that 
of black-and-white newsreels, as our 
reference value, we start with 1 foot- 
lambert for the screen in action. We 
can allow one tenth of that, 7 so long as 
it is very uniformly distributed, as the 
steady brightness of the walls, ceiling, 
and floor of the auditorium. That is, 
these surfaces may have a brightness 
of 0.1 foot-lambert. This brightness 
should be carried right up to the edge 
of the screen. Fabir Birren reports 
to the writer that when the space be- 
tween screen and proscenium arch was 
lighted in experiments in the Walt 
Disney studios the illusion of great 
depth was created in the pictures. 
This area should be lighted so as to 
appear as a pale gray mist. The 
lighting preferably should be abso- 
lutely uniform, but if that cannot be 
accomplished because of job condi- 
tions, then the brightness should be 
least near the screen, and rise to the 
brightness of Vio foot-lambert of the 
auditorium walls. This is not much 
light but it is close to what the Park 



4 

c - 



6 LOGAN July 

Avenue Theater, New York City, provides for full house lighting 
with no picture running, for example. Measurements in this modern 
theater with house lighting on full gave the following : 

Foot-Lamberts 

Walls 0.120 

Balcony face 0.085 

Ceiling 0.070 

Offhand, it would seem that the house lights in this theater therefore 
could be operated at all times with great improvement to the ease, 
comfort, and safety of the patrons. Perhaps the principal reason why 
this may not be true, is that the auditorium is largely lighted by coves. 
It is impossible to control the action of coves. The wall area in the 
immediate neighborhood of these coves has a brightness of 10 foot- 
lamberts. m This means that the cove running around the proscenium 
arch, for example, which is one of the main sources of light in this 
auditorium, is nearly ten times the brightness of the screen when a 
black-and-white newsreel is running; and 500 times the minimum 
screen brightness that can be expected. Jones 5 found that a bright- 
ness of 3 foot-lamberts was the highest that could be tolerated toward 
the front of the auditorium. 

In addition to this, the ceiling roundels that helped provide the 
house lighting had a brightness of 600 foot-lamberts. This is not so 
important as the cove brightness because these roundels are not in- 
cluded in the field of view of most people on the auditorium floor and 
would be disturbing principally to occupants of the balcony. The 
significant point is that the brightness of these ceiling roundels is a 
function of the size of lamp used, and the latter is larger than neces- 
sary because the reflection factors of the various surfaces reached by 
the light are too IOAV. If higher reflection factors for floor walls, and if 
the backs of seats were used, the lamps could be reduced in proportion, 
and the brightness of the roundels could be dropped to more reason- 
able figures. 

It is evident that in order to attain satisfactory house lighting 
while the screen is in action, the distribution of light must be very 
carefully controlled, as the brightness level of 0.1 foot-lambert must 
be the actual maximum brightness at any point within 30 degrees of 
the line of sight of a patron watching the screen (see Fig. 3). This 
control not only will involve the careful selection of location of the 
light sources, but also the careful choice of materials for walls, ceiling, 



1948 



BRIGHTNESS AND ILLUMINATION REQUIREMENTS 



and floor, to reflect the proper quantity of light efficiently, and so per- 
mit the use of small lamps in order to have equipment of very low 
brightness. 

This problem will ease somewhat as screen brightnesses become 
higher. If, for example, colored films replace black-and-white en- 
tirely, house lighting can about double, as indicated by the figures in 
the last column of Table II. 

That there is a need for house lighting is evident. Patrons of mov- 
ing picture theaters are coming and going constantly. The lack of 



pjihSPECTIVji OF ' A HXPOTHiTICALLX , 
VERAGE-, MOTION PICTURE HOUSE 




Fig. 3 All that is included in the field of view of a patron seated in the 
standard observer's position. 

light handicaps safe movement and causes inconvenience, not only to 
the patrons who are moving in and out of seats, but to those with 
whom they interfere because they cannot see sufficiently well to move 
with the least disturbance. 

Illumination levels in moving picture theaters with the house lights 
out are somewhere between starlight and moonlight, and much closer 
to the former than the latter. Under these conditions accidents will 
average seven times the theoretical minimum rate. 8 There is no 
possibility that accidents can be reduced to the theoretical minimum 
rate in the foreseeable future as a general brightness of the field of view 
of 6 f oot-lamberts would be required, or sixty times the maximum that 



8 



LOGAN 



July 



present screen brightnesses will permit. However, the adoption of a 
general brightness level of 0.1 foot-lambert would tend to reduce acci- 
dents by about 43 per cent over present experience, which would be a 
worth-while gain. 

Second, the lack of sufficient general light invites undesirable con- 
duct on the part of some members of the audience, particularly chil- 
dren and young people. 

TABLE II 

COMPARISONS OF AVERAGE BRIGHTNESS MEASUREMENTS OF MOTION PICTURE 

SCREENS 

Brightness of Screen 
with Film Running as 

Average Brightness a Percentage of Blank 
in Foot-Lamberts Screen Brightness 

Screen Film Group 

Film Blank Running Net Average 



Black-and-white news 


15.0 


.08 


7 




Black-and-white feature 


15.0 


.09 


7 


8 


Black-and-white news 


13.6 


.42 


10 




Cine-color short 


15.0 


.40 


9 




Technicolor feature 


10.1 


.27 


13 




Technicolor travelog 


15.0 J 


J.40 


16 


15 


Self-colored animated cartoon 


10.1 


L.65 


16 




Self-colored animated cartoon 


15.0 J 


J.80 


19 





Third, it reduces the comfort of patrons. Vision is tolerable in 
most moving picture theaters but all authorities agree that, with a few 
notable exceptions, it is far from comfortable Television manufac- 
turers have been faced with this comfort factor and have found it 
necessary to raise television screen brightness so that the screen can 
be viewed in domestic interiors with house lights on. 

Last, house lighting inspires and aids better "housekeeping," which 
patrons find inviting. 

A brightness of 0.1 foot-lambert is too low for people to adapt to 
quickly when coming from outdoors, unless a long foyer is available in 
which the lighting can drop steadily as the people move along. How- 
ever, some improvement in the situation can be brought about in any 
case if the brightness of the foyer surfaces at the theater end is set at 2 
foot-lamberts. This should be succeeded by a brightness of 1 foot- 
lambert for the surfaces of the extreme rear of the auditorium behind 



1948 BRIGHTNESS AND ILLUMINATION REQUIREMENTS 



>> ^GttTune'-L'l 

. / u\ 




SECTION 



OBSERVERS POSITION FOR 
ILLW1INEERING PERSPECTIVE 



PLAN 




Fig. 4-^-Section gives sight lines of closest and farthest observer, and of 
observer in standard position. It also shows the 30-degree angle with sight 
lines and that no luminous part of any lighting unit comes within 30 degrees 
of sight line of any observer. Finally, it shows that no direct light from a 
lighting unit can reach the screen. Figures 0.1^ etc., show recommended 
brightness levels in foot-lamberts. 



10 LOGAN July 

the last row of seats (the crossover) . This 1 f oot-lambert brightness 
should drop to 0.5 f oot-lambert on the aisle floors within 10 feet of the 
rear end of the aisle, and to the prevailing 0.1 f oot-lambert within 20 
feet. From then on, up to the front of the auditorium, the floor 
brightness of the aisles should remain at 0.1 f oot-lambert. This ar- 
rangement of brightnesses is illustrated in Fig. 4, with a suggested ar- 
rangement of lighting outlets to accomplish it. 

Higher house brightnesses would be possible if motion picture thea- 
ters were designed to permit them. This might sometimes require 
the screen to be louvered or hooded (after the fashion of traffic lights, 
or the miniature screens used for sales promotion in camera stores). 
Offhand this would appea r to reduce the number of seats by narrowing 
the angle of view, but this would not be necessary as the principal 
louvering would be against the ceiling to prevent direct light from the 
ceiling lights striking the screen. The actual amount of hooding re- 
quired could also be reduced by sinking the lights into the ceiling, so 
that the depth of the coffer acted as a louver against the screen (see Figs. 
3 and 4) . This would have the advantage of hiding the main ceiling 
lights from the balcony patrons. An examination of Figs. 3 and 4 
will show that such ceiling lights in the main ceiling cannot come into 
the field of view of any patron on the main floor as long as none n re 
placed in the forward 30 per cent of the ceiling. This prohibition also 
prevents stray light from any of the ceiling sources reaching the 
screen. Figs. 3 and 4 also show that the lights in the main ceiling, 
and those in the balcony soffit, when recessed in properly design e 1 
coffers, are hidden from most patrons. In the few cases where the 
lens can become visible it is at the upper edge of a patron's field of vi: w 
where it is farthest from the line of sight, and the least effective 1 in re- 
ducing visual efficiency and comfort. The sides of the light coffers 
should be painted a dark gray to prevent them being bright enough to 
disturb patrons. Concealed downlights also could be used. In 
many theaters the use of lens units in coffers, or downlights, would be 
sufficient, in combination with the fact that screens are usually placed 
6 to 10 feet behind the proscenium arch, to make special louvering of 
the screen unnecessary. 

In addition to this it would be desirable to give all surfaces that are 
parallel to and face the screen, such as the balcony face and rear wall 
of the theater, a low reflecting finish (about 20 per cent), to make their 
contribution to screen brightness neglibible. Surfaces parallel to, but 
that face away from the screen, such as the backs of the seats, should 



1948 BRIGHTNESS AND ILLUMINATION REQUIREMENTS 11 

be given a reflection factor about equal to floor, or 30 per cent. 
Finally, the walls and ceiling should be sloped away from the screen as 
far as possible and given a ribbed surface. One side of each rib should 
face away from the screen and be given a reflection factor of 50 per 
cent. The other side of the rib that would face in the general direc- 
tion of the screen'could be dark gray with a 10 per cent reflection fac- 
tor. This permits light to be accepted by these surfaces without its 
getting back to the screen. Floor coverings should have a reflection 
factor of 30 per cent and ceiling lights should begin no closer to the 
screen than about one third the depth of the house. They would be 
arranged over the remaining two thirds of the ceiling over the aisles 
so that the aisles would get the benefit of the principal illumination and 
no patron could be directly under a light to receive a high light on 
back of head and shoulders that might be disturbing to others. This 
would usually also light up the walls owing to the side aisles running 
along the walls. Where there are no side aisles the lights should also 
run in such relation to the walls as to light them uniformly. 

Similar lights should be repeated under the balcony over the aisles, 
and along the back crossover. 

Illumination on the ceiling would come from diffusion from the 
walls and floor. If ceiling was finished white it would acquire a 
brightness about equal to moonlight. 

It would be desirable to raise this brightness to Vio of a foot-lam- 
bert but most attempts to do this raise more problems than they 
solve. Where the scale of the interior permits, as in Radio City 
Music Hall, it can be done by a similar series of well-designed stepped 
coves. This is impractical in the average motion picture auditorium, 
and it is better to let the ceiling remain dark than to run into the great 
brightness variations that accompany most attempts at ceiling 
illumination. 

It is easier to meet the visual requirements of continuous motion 
picture theater lighting with incandescent lamps than with fluores- 
cent, as the extraordinary degree of control required is difficult with 
fluorescent. Fluorescent can be used for the decorative and inter- 
mission lighting. Further, the incandescent equipment can be 
dimmed easily so that after the computed installation is made, the 
exact point at which the house lighting no longer handicaps the 
screen can be determined by experiment. 

In conclusion, the brightness level of 0.1 foot-lambert suggested in 
this paper for house lighting (about three times full moonlight), 



12 LOGAN 

would call for an illumination level of from 0.3 to 0.4 foot-candle, on 
the basis of the reflection factors recommended This can be secured, 
from 60-watt, incandescent lamps on about 15-foot centers average, 
in controlled, coffered, direct-lighting equipment. Where the bright- 
ness level is to rise ; as at the rear stretch of the aisles, and the rear 
crossover, the lights should be spaced proportionately closer. If 
these incandescent lamps were used behind a Controlens the glass 
surface could have an off-axis brightness of as low as 60 foot-lamberts, 
instead of 600 which is present practice. Even this low equipment 
brightness of 60 foot-lamberts would not come into the normal field of 
view, owing to the coffer shielding, as previously explained. 

Now that the nature of the problem is understood, designers can be 
depended upon to come forth with a variety of layouts and equipment 
that will meet the conditions. 

REFERENCES 

(1) "Report of screen-brightness committee," /. Soc. Mot. Pict. Eng., vol. 
50, pp. 260-274; March, 1948. 

(2) "I.E.S. Lighting Handbook," Illuminating Engineering Society, New 
York, New York, 1947, p. 2-2. 

(3) "The brightness ratio of the visual task" (ex. gr., the screen) "to its im- 
mediate surroundings should be no greater than three." From "Brightness and 
brightness ratios," Report No. 1 of the Committee on Standards of Quality and 
Quantity for Interior Illumination of the Illuminating Engineering Society, 
Ilium. Eng., vol. 39, pp. 713-723; December, 1944. 

(4) F. M. Falge and W. D. Riddle, "The lighting of motion picture audi- 
toriums," /. Soc. Mot. Pict. Eng., vol. 3, pp. 201-212; February, 1939. 

(5) L. A. Jones, "The interior illumination of the motion picture theater," 
Trans. Soc. Mot. Pict. Eng., no. 10, pp. 83-96; 1920. 

(6) M. L. Luckiesh, "Reading as a Visual Task," D. Van Nostrand Company, 
Inc., New York, New York, 1942, p. 23. 

(7) This relationship of 10 to 1 for screen brightness to surrounding brightness 
(or auditorium brightness), is based on Lythgoe's research as reported by Parry 
Moon in "The Scientific Basis of Illuminating Engineering," McGraw-Hill 
Book Company, Inc., New York, New York, 1936, p. 441. 

(8) H. L. Logan, "The role of lighting in accident prevention," Elec. Eng , 
vol. 62, pp. 143-147; April, 1943. 



Light Modulation by P-Type 
Crystals* 

BY GEORGE D. GOTSCHALL 

BRUSH DEVELOPMENT COMPANY, CLEVELAND, OHIO 



Summary A means of modulating a light beam with a flat response 
which greatly exceeds the audio range is described utilizing the linear 
electrooptic effect in P-type** crystals. The unit uses parallel polarized 
light and although it requires relatively high voltages, it draws essentially 
no current and has no moving parts. From the basic aspects it seems very 
promising for an efficient yet sturdy variable-density recording system. 



INTENSITY MODULATION of a light beam may be accomplished in one 
of three or more ways: (1) mechanical shutter or diaphragm, (2) 
modulation of intensity of the light source proper, or (3) phase 
retardation of polarized light passing through an electrooptic medium. 
The first two methods are quite well known, but the third, although 
not new in principle, is relatively new in application. The quadratic 
electrooptic effect, also known as the Kerr effect, has been known to 
scientists for some tune, especially in such polar liquids as nitro- 
benzene. However, the effect is small, voltages are extremely high, 
the light beam is restricted in width, and the cell is liquid in form. 
The effect to be described herein is the so-called linear electrooptic 
effect which is a property characteristic of piezoelectric crystals and 
which overcomes the Kerr-cell disadvantages wholly or in part. 
The basic symmetry relationships of the linear electrooptic effect 
were first discussed by Pockels, 1 who made detailed measurements on 
quartz, sodium chlorate, tourmaline, and Rochelle salt. This work 
is still basic for our knowledge of the electrooptic effect in crystals, 
although during the last fifteen years several German scientists have 
published articles on this phenomenon with emphasis on the applica- 
tion of zinc sulfide. 

* Presented November 19, 1947, at the Atlantic Coast Section Meeting in 

New York. 

** The term "P-type" has been given to a group of isomorphic crystals which 

include the primary phosphates and arsonates of ammonium, potassium, or 

rubidium. 

JULY, 1948 JOURNAL OF THE SMPE VOLUME 51 13 



4 GOTSCHALL July 

The requirements which a crystal must meet in order to be suitable 
electrooptically are many, and as a result only a few crystalline sub- 
stances are satisfactory. Extensive research at the Brush Develop- 
ment Company led to the discovery of a substantial electrooptic 
effect in ammonium dihydrogen phosphate crystals as well as other 
crystals of the primary phosphate family, termed P-type. It was 
recognized that the symmetry relationships in this crystal family 
were particularly favorable for the occurrence of a sizable parallel 
electrooptic effect, i. e., with the light beam parallel to the electric 
field. Among the outstanding features of these crystals are the facts 
they can be artificially grown to large sizes, have excellent trans- 
mission characteristics, satisfactory physical properties, and possess 
the highest electrooptic constants. 

To explain briefly the nature of the parallel electrooptic effect, 
first consider the mechanics of light transmission through a trans- 



PARALLEL LIGHT SOUJBCC CRYSTAL ANALYZER (P ) 




\f , I 

1 I 

Ij JL | t _-z LJGHT BEAM 

/ / 

POL ABIZEB (P,) V* BETABDA TlON SHEET 

(WHEN USO) 

Fig. 1 Simple electrooptic, system. 

parent substance. Transparent media are composed of atoms or 
molecules carrying electric charges or dipoles. The refraction (or 
velocity) of light is then determined by the disposition and electro- 
magnetic interaction of these particles with the electric-field com- 
ponent of the incident light wave. The application of an electric 
field to the transparent medium will produce displacement or deforma- 
tion of the particles and thereby influence the refractive properties 
of the material. In the case of the P-type crystals, a certain cut and 
alignment allows light to pass with equal velocities for all planes of 
polarization. However, the application of an electric field reduces 
the phase velocity in one specific plane of polarization and increases 
it in a perpendicular plane of polarization, thus introducing a phase 
difference in the two components. The parallel electrooptic effect 
may then be described as a linear change of the refractive indexes 
(or phase velocities) for a giyen applied electric field. This change is 



1948 



LIGHT MODULATION BY P-TYPE CRYSTALS 



15 



at best in the order of one part per million for a field of one kilovolt 
per centimeter, but even this minute change is satisfactory for a 
device based on phase shifts. 

To explain the behavior a bit more fully, let us consider a simple 
system (Fig. 1) where we polarize a parallel light beam so that the 
vibration direction is parallel to one of the crystalline axes, X or 
Y, (mutually perpendicular to the Z or optic axis in P-type crystals) . 
This light beam can be resolved into two vector components along- 
secondary axes X and ? (also called mechanical axes) (Fig. 2). In 



A 

X 



45 



A' 

Y 



Fig. 2 Z-0 Plate of "PN" crystal showing position of 
polaroids and secondary axis. 

this figure, the polarizer (P^) is shown as parallel to the Y axis and 
the analyzer. (P 2 ) parallel to the X axis. Initial conditions will 
permit no light to pass, for we have the analyzer at 90 degrees to the 
polarized beam. However, under the influence of an electric field, 
the velocity of the vector components along X and Y are changed, 
one being increased and the other decreased, the effect on each 
depending on the polarity of the voltage. This results in incomplete 
extinction of the light, which will now be visible through (P 2 ). 
The electrooptic effect will be maximum for the light polarized 
parallel to one of the crystalline axes, X or Y (as shown in the above 



16 



GOTSCHALL 



July 



diagram) and minimum for light polarized parallel to one of the 
secondary axes, X or ?. 

For a field of one kilovolt per centimeter, the difference in the 
two refractive indexes was found to be 2.9 X 10 ~ 6 , or equivalent to 
a phase difference of about Tr/20 radians per centimeter for green 
light. The intensity of the light passed is found to be proportional 
to the sine squared of half the angular phase difference. For a 
"PN"* (ammonium dihydrogen phosphate) crystal as discussed we will 
get maximum transmission for a retardation of one half wavelength 
which requires approximately 9000 volts for green light (Fig. 3). 
For the system as described, thickness of the crystal does not enter, 




VOL TA GE APPL /ED 

O.C. K^LOVOLTS 



Fig. 3 Light intensity versus direct, kilovolts for "PN"-Nesa unit using 
green parallel light and crossed polaroids. 

as doubling the thickness for a given voltage will result in half the 
change of refractive index but twice the light path. 

The value of the change in refractive index as given above for "PN" 
is the total electrooptic effect which is composed of the "clamped" 
electrooptic effect and the "indirect" electrooptic effect. This latter 
effect is created by the piezoelectric deformation of the crystal lattice 
which causes a refractive index change through the elastooptic effect. 
In the P-type crystals these effects are of the same sign, and recent 
experimental data have shown the division in "PN" to be 58 per cent 
"clamped" and 42 per cent "indirect." 
* Copyright, Brush Development Company, Cleveland, Ohio. 



1948 



LIGHT MODULATION BY P-TYPE CRYSTALS 



17 



Theoretically, the "clamped" electrooptic effect is frequency- 
independent practically to the infrared region because displacements 
in the order of only intermolecular distances are involved. The 
"indirect" effect has resonant frequencies dependent upon the phys- 
ical dimensions. It is to be expected then that this effect would 
become negligible above the range of natural resonant frequencies of 
the crystal. The frequency curve is shown in Fig. 4 and it is to be 
noted that the slight increase in response at the high end is due to 
approaching resonant frequency. Mechanical damping will elimi- 



/o.ooo 20.000 



Fig. 4 Frequency response of light modulator using a 
150-volt, root-mean-square, sine wave. White, parallel, 
direct-current light source was used with X/4 plate inserted 
between the crossed polaroids. 

nate this rising characteristic. The linearity of modulated output 
versus modulation voltage is shown as Fig. 5. 

When using the unit as a light-beam modulator, it is usually de- 
sirable to use an optical bias of a quarter-wave retardation. As 
shown in Fig. 3 ; this transfers the initial operating point from the 
origin to point X with no voltage applied. Operating from this point 
of the curve it can be seen that we get maximum modulation and 
minimum distortion for a given applied audio voltage. In most of 
the frequency experiments, a modulating voltage of 150 volts, root- 
mean-square (425 volts peak-to-peak) was used with very satis- 
factory results. 

A convenient size of crystal for experimentation was found to be 



18 



GOTSCHALL 



July 



1 



2 inches square and about Vie inch thick. After polishing to an 
optical finish, transparent conducting electrodes, Nesa,* are at- 
tached by means of a special transparent conducting cement. The 
Nesa electrodes are l 3 / ]6 inches square, thus providing a nice margin 
of crystal to act as high-voltage insulation. This margin is treated 
to prevent damage by moisture and consequent leakage or voltage 
flashover; The unit easily accommodates a 1-inch diameter parallel 
light beam. The static capacity of such a unit is under 100 micro- 
microfarads, diminishing rap- 
idly in the resonant frequency 
region. The direct-current 
shunt resistance is in the order 
of 150 to 350 megohms. 

The transmission of the 
over-all system depends 
chiefly upon the transmission 
of the polarizing material and 
the transparent electrodes as 
the transmission of "PN" is 
practically 100 per cent from 
2000 angstrom units to 1.5 
microns. The transmission of 
a recently completed unit 
composed of "PN" crystal 
and two Nesa electrodes ce- 
mented onto place was about 
75 per cent whereas the Polar- 
oid** had 28 to 32 per cent 
transmission when it ideally 
should be 50 per cent. This 
results in an over-all maxi- 
mum transmission value of 
about 15 per cent for half-wave retardation which is more than enough 
to activate a photoelectric cell or expose film. 

The dark-to-light ratio depends upon many factors mentioned 
above plus alignment and beam parallelism and color. However, 
dark-to-light ratios as high as 300 to 1 have been obtained with the 
application of 9 direct kilovolts. Alignment of the crystal with 

* Made by the Pittsburgh Plate Glass Co., Pittsburgh, Pa. 
** Made by the Polaroid Corporation, Cambridge, Mass. 



so 



/OO0 O0O 3OOO 
VOLTAGE APPLIED 

A.C. VOLTS (P. TOP.) 



Fig. 5 Linearity of modulator using 
"PN" crystal driven at 1000 cycles. 
Direct-current parallel light with X/4 
plate inserted. 



1948 



LIGHT MODULATION BY P-TYPE CRYSTALS 



19 



SIGNAL 'VOLTAGE 




-LAMP POWER 



Fig. 6 Assembled view of experimental light modulator. 

relation to the light beam is very critical and is done with the assist- 
ance of a projection lens. 

A complete system including the light source and lens system was 
constructed in a housing 2 1 / 2 X 4 X 5Y 2 inches. As a light source, 
a 10-watt Western Union concentrated arc lamp 2 was used and 



r~ ANALYZED AND 
APZ&TU8E 




Fig. 7 Exploded view of experimental light modulator. 



20 GOTSCHALL 

operated from two heavy-duty 45-volt B batteries in series. A 
portable high-voltage supply was first used to strike the arc, and 
later to apply voltage to the crystal unit. Since the lamp will remain 
lit at reduced current, a stand-by switch reduces the current by 80 
per cent except when actually in use. A photograph of this unit is 
shown in Figs. 6 and 7. Although the point light source is conven- 
ient in size, in the laboratory suitable parallelism was obtained from 
an inexpensive Central Scientific light source having a 6-volt, 18- 
ampere tungsten filament. Direct current from a bank of storage 
batteries was supplied for frequency measurements while 60-cycle 
alternating current was used for all other tests. 

The unit as described has a flat response in excess of audio fequire- 
ments, has an excellent dark-to-light ratio, is simple and sturdy, 
has no moving parts, has a high impedance input, and has good 
transmission characteristics for application to variable-density sound- 
on-film recording. The adaptation is very simple as light emanating 
from the aperture of the modulator as shown in Fig. 7 is parallel, 
and a cylindrical lens could then focus this circular beam of modu- 
lated light into a small slit on the sound track. 

REFERENCES 

(1) F. Pockels, "Electro-Optisches Verhalten Piezoelektrisher Kristalle," 
Goettingen Abhandlungen, vol. 39, 1894. 

(2) W. D. Buckingham and C. R. Deiberf, "Characteristics and applications 
of concentrated-arc lamps," /. Soc. Mot. Pict. Eng., vol. 47, pp. 376-400; Novem- 
ber, 1946. 



FORTY YEARS AGO 

Talking Pictures in Rochester 

This is the way the press agent describes the animated pictures: "To 
hear the voice, to catch every sound and the intonation of every word 
and see the people in life size moving before your eyes, and yet realize 
there is not a single person there it seems like some phantom of the 
brain, an hallucination, and one is almost tempted to rush to the stage 
and grapple with the ghostly actors as one is moved to cry out in the 
vividness of a dream. Such is the wonderful spell that is cast over the 
spectator on his first view of the marvelous talking, singing, dancing 
moving pictures which Manager Parry of the National will introduce 
for the first time in Rochester to-morrow afternoon." 

The Moving Picture World, May 30, 1908 



Portable 16-Mm Sound Projector 

BY H. H. WILSON 

AMPRO CORPORATION, CHICAGO, ILLINOIS 



Summary Some of the problems encountered in the design and pro- 
duction of a quality 16-mm sound projector designed to meet the require- 
ments of the school, church, and industrial fields, are analyzed. Screen 
illumination, sound reproduction, operational controls, film handling and 
film protection, noise factors, styling, maintenance, and weight limitations 
will be discussed. Manufacturing problems and their solution on the basis 
of mass production will be considered. 



THE PROJECTOR described was designed to meet the requirements 
of the school, church, and industrial fields. First, the general 
conditions under which the equipment will be used; second, the 
consumers' requirements; and third, the actual design and manu- 
facture of a projector to meet these requirements will be described. 

The Application The school, church, and certain phases of in 
dustrial applications can be considered as a group so far as the design 
of this type of equipment is concerned because of the technical simi- 
larity of their application^ of the equipment. In most cases the 
projector will be used to project sound films before small audiences 
although occasionally it will be used before audiences of 500 to 600 
people. 

Classrooms usually have hard-surfaced walls and frequently cannot 
be completely darkened. Industrial showings may be made in 
many types of rooms ranging in size and acoustical properties from 
the private office to the product display room. 

Consumer Requirements Since we have considered the general 
conditions under which this equipment will be used, let us now turn 
to a more detailed analysis of what will be required in the projector 
in order to make it most useful as an audio-visual tool. 

The distance from the last row of seats to the front of the typical 
classroom is about 25 feet; therefore the screen width should be 
approximately 4 feet (a 39- X 52-inch screen is commonly used). 
This screen has an area of 14 square feet, consequently, at least 
165 lumens will be required to provide adequate screen illumination. 

* Presented April 25, 1947, at the SMPE Convention in Chicago. 

JULY, 1948 JOURNAL OP THE SMPE VOLUME 51 21 



22 WILSON July 



a few watts of audio power would be required for the class- 
room, but additional power will be required for larger rooms. In- 
creased power can be obtained at a reasonable cost, so it was con- 
sidered advisable to provide an amplifier having 10 to 15 watts' 
output. Sound quality should be as good as space, weight, and 
cost factors will permit. 

The projector frequently will be operated by elementary or high- 
school pupils; therefore, the controls should be as few and as acces- 
sible as possible. It will be necessary to provide for both sound and 
silent speeds, reverse operation, and the projection of a single frame. 
Simplicity of threading is required as well as maximum film 
protection. 

Due to the excessive area of hard-surfaced Avails, the mechanism 
must be very quiet in operation or the attention of the audience will 
be distracted from the subject matter being presented. 

Naturally, audio-visual equipment will be used only for those 
applications where either it can do a better teaching job or a more 
economical one than can be accomplished by other means; conse- 
quently both the initial cost of the equipment and the maintenance 
cost must be kept as low as is practicable. The design of the pro- 
jector should be such as to provide maximum film protection because 
first, the cost of procuring or replacing prints is a factor in the' cost 
of a visual-education program, and second, the teaching film differs 
from the entertainment film in that the contents of the teaching 
film does not become obsolete for many years; consequently, film 
wear is the principal cause for retirement of a print. 

For ease of carrying and storage it is desirable that the unit be as 
small and compact as possible and that neither the projector nor 
speaker case, when packed, weigh more than 50 pounds. 

General Design In the design of the Premier-20 projector great 
effort was made to meet the consumer's requirements. The com- 
plete design cannot be said to be entirely new; those units, which 
past experience indicated to be satisfactory, were retained in this 
model, some units have been redesigned, and the methods of manu- 
facturing other units have been revised in order to maintain closer 
tolerances and thereby improve their performance. 

Light Source and Optics The projector was designed to use pro- 
jection lamps of the medium prefocused base type. A 750-watt, 
25-hour lamp is standard equipment although a 1000- watt lamp may 
be used. The lamp socket is mounted in such a manner that the 



1948 



PORTABLE 16-MM SOUND PROJECTOR 



23 



lamp can be moved either vertically or horizontally. This type of 
mounting provides two advantages, one, positive alignment of the 
lamp filament with the optical axis can be obtained, and two, the 
lamp position can be adjusted in order to correct for the shifting 
of the filament which may result from use. 

The reflector and condensing lenses are mounted on the right- 
hand cover of the projector and the holder is properly positioned on 
the cover at the time of assembly. The cover assembly and its optical 
components may be removed for cleaning and replaced without dis- 
turbing their alignment with the aperture. 




Fig. 1 Intermittent and shutter. 

The projection-lens mount is solidly attached to the mechanism 
head by means of a dowel and screws in order to maintain positive 
alignment of the lens with the aperture plate. Coarse focusing of 
the projection lens is obtained by sliding the lens in the holder^ fine 
focusing, by rotation of the threaded lens barrel. The lens is locked 
in position by means of a cam-and-spring assembly which clamps 
the lens in position without producing any tendency of the lens to 
shift in the holder. A coated //1. 6 lens of 2-inch focal length is 
standard equipment. Lenses of other focal lengths also may be used. 

Intermittent and Shutter (Fig. 1) The intermittent unit consists 
of three cams and a shuttle. Two of the cams make up the lateral 



24 WILSON July 

cam assembly (6) which causes the teeth of the claw to engage the 
perforations and also holds the shuttle (2) and claw in the retracted 
position while the shuttle makes an idle stroke. The purpose of the 
idle stroke is to allow the vertical cam (8) to be revolved at 2880 
revolutions per minute (at sound speed) thereby providing a com- 
paratively short film-transport time without the use of a vertical 
cam havdng such a small working angle that the life of the inter- 
mittent might be seriously affected. The film-transport time is 
4.68 milliseconds, therefore, approximately 1 / B of the complete 
projection cycle is required for film advance. Each lateral cam is 
ground individually and then paired with the mating cam by selective 
assembly. The vertical cam is rough-ground, then attached to the 
camshaft; and finish-ground in order to maintain the throw within 
close limits. 

The action between the claw and the film perforations is quite 
similar to that of a rack-and -pinion mechanism. The radius of the 
pinion (distance from shuttle pivot (1) to film plane) is quite long 
and the tooth form has been corrected in order to eliminate any 
tendency of the claw teeth to drag across the edges of the perforations 
during the entrance or retraction periods. This type of movement is 
very quiet and produces very little film slap; it also has the advantage 
that when used in conjunction with the gate mechanism, which will 
be described, it will not damage the perforations if the lower loop 
is lost, and the loop can be reset without stopping the projector. 

The two-blade barrel-type shutter (4) revolves at 2160 revolutions 
per minute at sound speed and provides three interceptions of the 
light beam per frame. The shutter is attached to an adjusting disk 
so that exact timing with the intermittent can be obtained. The 
shutter is driven by means of a quill through which the safety-shutter 
shaft passes. The safety shutter (5) consists of a single curved blade 
having a radius shorter than the intercepting shutter and pivoted 
on the axis of the intercepting shutter. The single hole pierced in 
the safety shutter acts as an optical stop and maintains a low aperture 
temperature when still pictures are being projected. The safety 
shutter is actuated by means of a centrifugal clutch mechanism which 
is built into the shutter-gear assembly. 

Framer and Film Gate Framing is accomplished by the vertical 
movement of the framer plate which slides in a milled channel directly 
behind the aperture plate (Fig. 2). In assembly the aperture plate 
is aligned with the aperture in the framer plate and is attached to 



1948 PORTABLE 16-MM SOUND PROJECTOR 25 

the mechanism head by means of six screws. The right-hand edge of 
the aperture plate is used for film-positioning and springs located on 
the opposite edge of the plate hold the film against the right-hand 
edge. 

The pressure shoe (1) is attached to the pressure-shoe carrier 
(2) which slides in ways milled in the carrier yoke (3). The carrier 
yoke is pivoted near the front of the projection-lens mount and is 
locked to the lens mount by means of a latch (4) located near the 
rear of the lens mount. Moving the gate lever to its forward position 
moves the pressure-shoe carrier and the pressure shoe away from the 




Fig. 2 Lens-mount assembly. 

aperture plate and simultaneously opens the sprocket shoes. Press- 
ing the gate latch toward the aperture releases the carrier yoke so 
that the yoke and pressure shoe can be swung outward approximately 
90 degrees. This makes both the pressure shoe and the aperture 
plate readily accessible for cleaning. 

Pressure is applied to the pressure shoe by means of two coil 
springs of conical form. Control of the shoe pressure is obtained by 
movement of the carrier stop (5). The contact surface of the shoe 
is 3Vs inches in length; this results in a low pressure per unit of area; 
consequently, if the lower loop is lost, both the film and the shoe are 



26 WILSON July 

pushed away from the aperture by the claw and the film is not 
damaged. Lateral alignment of the pressure shoe is obtained by 
moving the mounting plates (6) by means of which the shoe is at- 
tached to the carrier. 

Bearings, Lubrication, and Gearing All shafts in the mechanism 
are parallel; consequently, the bearing bosses can be reamed in a 
single fixture thereby simplifying the manufacturing procedure and 
maintaining a high degree of precision. "Oilite" bearings are used 
for all shafts and are burnished to size after they are pressed into the 
mechanism casting. 

All moving parts of the mechanism receive oil from a central oil 
well. Oil is distributed to various parts by means of oil tubes which 
are sealed into the oil well and bearing bosses. The shuttle and 
bearings that are not parts of the mechanism housing receive oil 
through oil passages drilled axially in the shafts and holes drilled 
radially in the shafts at the proper points. 

The gearing is of the helical type. All transmission members 
lie within four parallel planes which are closely spaced. This type 
of design produces a very compact transmission assembly in which 
end thrusts can be kept low, a high degree of precision can be main- 
tained, and gear noise and vibration can be reduced to a minimum. 

Motor and Drive Unit The drive motor is of the universal type. 
A Lee governor is used to control both the sound and silent speeds. 
The speed-selector switch and reversing switch are attached to the 
motor by short leads and are located on the amplifier-housing wn.ll 
adjacent to the motor. The complete motor assembly can be re- 
moved by disconnecting two leads from the terminal board on the 
motor, removing the motor-retaining parts, the switch-retaining nuts 
and the fan. 

The main drive system consists of a flat, neoprene-impregnated, 
fabric drive belt running on pulleys having synthetic rubber facings. 
The driven pulley is mounted on an "Oilite" bearing and also serves 
as the driving member of a single-plate automotive-type clutch. The 
clutch mechanism is actuated by means of a knob on the right-hand 
cover of the projector. The purpose of the clutch is to disengage 
the projector mechanism from the motor in order to project single 
frames. 

Ventilation A radial-blade centrifugal fan is mounted on the 
motor-armature shaft. The fan .is 3Vs inches in diameter and oper- 
ates at the motor speed of 5200 revolutions per minute when the 



1948 PORTABLE 16-MM SOUND PROJECTOR 27 

projector is running at sound speed. Air is drawn across the ampli- 
fier and motor and into the fan intake thereby providing ventilation 
for the amplifier and motor. A fan-scroll reversing vane is used to 
maintain substantially the same air delivery regardless of the direction 
of fan rotation (1). 

Feed and Take-up Mechanisms The feed-reel arm is permanently 
attached to the mechanism housing and is pivoted in order that it 
may be swung back over the top of the mechanism when the pro- 
jector is placed in the case. When the projector is operated in 
reverse a ball-type clutch contained within the spindle cup auto- 
matically engages and the spindle is driven in a counterclockwise 
direction by means of a spring belt. High-speed rewinding is ac- 
complished by engaging a dog- type clutch located on the left-hand 
side of the mechanism. A pulley formed as an integral part of the 
clutch, by means of a spring belt, drives a pulley attached to the 
left-hand end of the reel spindle. Two thousand feet of film can be 
rewound in two minutes. 

The take-up-reel arm also is pivoted in order that it may be swung 
up in front of the mechanism housing when the projector is placed 
in the case. The take-up spindle is connected to the spindle-drive 
pulley through a ball-type clutch which automatically disconnects 
the spindle from the pulley when the projector is operated in reverse. 
For rewinding, the take-up belt is shifted to a loose pulley by means of 
a manually operated belt shifter. 

SoundheadThe soundhead is assembled as a separate unit and is 
attached to both the mechanism housing and the amplifier housing. 
Direct scanning is accomplished on a rotary sound drum mounted 
on ball bearings and stabilized by means of a flywheel. Loop vibra- 
tion is controlled by passing the film between the pressure and tension 
rollers. The pressure-roller arm is pivoted and its travel controlled 
in such a manner that it can be used to reset the lower loop without 
stopping the projector. 

Amplifier and Speaker The three-stage amplifier consists of a 
6J7 voltage amplifier, a 6J5 driver, and push-pull 6V6 output stage. 
The output is 15 watts with less than 5 per cent distortion. The 
standard output impedance is 15 ohms; a simple adapter (available 
as an accessory) makes necessary connections to the 7.5-ohm tap 
of the output transformer for operation of two speakers. A 6V6 
is used as a radio-frequency oscillator to provide 6 volts at 1 ampere 
for the exciter lamp. 



28 



WILSON 



July 



The volume control for sound on film controls the intensity of the 
exciter lamp; a potentiometer in the grid circuit of the 6J7 controls 
the volume of the microphone or phonograph. A slotted-shaft type 
of control, located in the rear control panel, controls the polarizing 
voltage applied to the phototube. The tone control is of the inverse- 
feedback type. 

Plug and receptacle connectors are located in the rear control panel 
for connecting a converter or inverter if required. The standard 



GATE RETRACTOR 
LEVER (I) 




PRESSURE 
ROLLER (2) 



Fig. 3 

amplifier was designed to operate on 50 or 60 cycles, 105 to 125 volts 
alternating current. A 25-cycle model is also available. 

Removal of the main nameplate provides access to the tube sockets 
for voltage checks. The amplifier may be removed by taking off the 
bottom cover, disconnecting four leads from terminal boards, and 
removing eight retaining screws. 

A 12-inch permanent-magnet dynamic speaker is used. The 
magnet weight is 4 x /2 pounds, and the voice-coil impedance is 15 
ohms. The speaker is mounted in a case 16 inches high, 16 inches 



1948 PORTABLE 16-MM SOUND PROJECTOR 29 

wide, and 9 3 /4 inches deep. Fifty feet of speaker cable is standard 
equipment. 

Simplicity of Threading Since the sprocket shoes open automati- 
cally when the film gate is opened it is only necessary to move the 
gate-retractor lever (1) to the forward position and move the pressure 
roller (2) to the rear position in order to prepare the projector for 
threading (Fig. 3). 

Size and Weight The above-described projector is packed in a 
case 21 Y 2 inches long, 16 inches high, and 9 3 /4 inches wide. The 
projector alone weighs 33V4 pounds. Packed in the case with 
accessories its weight is 50 pounds. The speaker case which also 
contains a 1600-foot reel and the power and speaker cables, weighs 
26 pounds. 

ACKNOWLEDGMENTS 

The writer wishes to acknowledge the assistance of Messrs. A. 
Shapiro, T. J. Morgan, A. S. Dearborn, and T. R. Neesley in the 
preparation of this paper. 

REFERENCE 

(1) A detailed description of the design and operation of this unit is con- 
tained in the paper "Design progress in an 8-mm projector," by Thomas J. Mor- 
gan, J. Soc. Mot. Pict. Eng., vol. 49, pp. 453-463; November, 1947. 



FORTY YEARS AGO 

Moving Pictures in Schools 

Moving pictures, as an aid to education, are now being utilized in the 
National Preparatory School, in the City of Mexico, where a machine 
of the latest pattern has been- installed. The pictures will illustrate sub- 
jects in geography, history, physics, morals, and manual training. 
Mexico is the second country to adopt the cinematograph as an educa- 
tional factor, Germany having been the first. 

The Moving Picture World, May 16, 1908 



Optical Problems in Large- Screen 
Television* 



BY I. G. MALOFF 

RCA VICTOR DIVISION, RADIO CORPORATION OF AMERICA, CAMDEN, 
NEW JERSEY 



Summary Optical problems in large-screen television are enumerated 
and present-day solutions of these problems are discussed. Details of one 
prewar and two postwar models of RCA large-screen projectors are described. 



OPTICAL PROBLEMS involved in producing large-screen television 
include: (1) choice of suitable source of picture; (2) choice of 
suitable optical projection system; (3) choice of a suitable screen to 
fit a particular auditorium; and (4) selection of proper ambient 
lighting in the auditorium. 

In the past a great number of solutions to the above problems have 
been suggested, some of them tried, and some demonstrated. Among 
these are various types of light valves, supersonic light cells, and 
mirror and lens drums, also Mangin mirrors, refractive and reflective 
optical systems, lens and mirror-type viewing screens, and many 
others. Also the so-called "intermediate" or "zwischen" film method 
has been proposed" and tried in the early thirties in Germany, aban- 
doned, and now is again under development in this country at the 
Radio Corporation of America and other laboratories. In the 
intermediate film method a television picture appearing on the face 
of a cathode-ray tube is photographed on motion picture film, quickly 
processed, and reproduced through a regular film projector. Of 
course there is a certain delay and a certain amount of instantaneity is 
lost. 

The llC A technical staff, while having investigated and tried most 
of the proposed methods, has directed its large-screen television de- 
velopment mostly along the lines of the combination of (1) high- 
voltage cathode-ray tubes; (2) reflective or "Schmidt" . optics ; 
and (3) directional viewing screens tailor-made to fit particular audi- 
toriums; in other words, "instantaneous" systems. 

* Presented October 23, 1947, at the SMPE Convention in New York. 
30 JULY, 1948 JOURNAL OF THE SMPE VOLUME 51 



LARGE-SCREEN TELEVISION 



31 



Before the war, RCA produced and publicly demonstrated in a 
regular theater in New York City a .large-screen television picture on 
a 15- X 20-foot screen. The equipment utilized a 7-inch projection 
cathode-ray tube operating at 70 kilovolts. The optical system was 
of the reflective or Schmidt type, using a 30-inch spherical mirror 
and a 22 1 / 2 -inch aspherical correcting lens. The general appearance 
of this equipment is shown in Fig. 1. 




Fig. 1 Prewar television projector utilizing 31-inch mirror. 



Since the war the RCA organization, basing its work on previous 
experience, chose to continue developments along the lines of the 
prewar prototype. Recent developments resulted in two types of 
large-screen television systems. The first, the auditorium type, 
utilizes a cathode-ray tube 7 inches in diameter operating at 50 kilo- 
volts. The optical system consists of a 21-inch spherical mirror and 
a 14V2-inch aspherical correcting lens. This system, having approxi- 
mately a 6- X 8-foot screen, was publicly demonstrated at the con- 
vention of the National Association of Broadcasters in Atlantic 
City last September and is being demonstrated at this Convention. 



32 



MALOFF 



July 




Fig. 2 Postwar television projector utilizing 
21-inch mirror. 

The second system, the theater type, makes use of a 15-inch cath- 
ode-ray tube operating at 80 kilovolts. The optical system consists 




Fig. 3 Postwar television projector utilizing 42-inch mirror. 



LARGE-SCREEN TELEVISION 




33 



Fig. 4 Principle of reflective projection system. 



of a 42-inch spherical mirror, and a 30-inch aspherical correcting 
lens. At present it is the largest Schmidt-type system in the world, 
since the 72-inch Schmidt telescope of Mount Wilson as yet is not in 
operation. Two 42-inch RCA-Schmidt systems have been completed, 
tested, and found to be up to expectations. These systems give 
pictures of 18 X 24 feet in size and will be publicly demonstrated in 




Fig. 5 Machine for grinding 42-inch mirror. 



34 



MALOFF 



July 



the next few weeks. The general views of the two systems are shown 
in Fig. 2 and Fig. 3. 

In general, the optical problem of large-screen television is to pro- 
duce on a given size screen a picture of sufficient high-light brightness, 
resolution, and tone gradation, so that nothing contained in the 
incoming signal is lost. The word "sufficient" has often been re- 




Fig. 6 Polishing 42-inch mirror. 

placed by "maximum obtainable." It is a pleasure to state that with 
the new projector the standard of the Society of Motion Picture En- 
gineers of 7 to 14 foot-lamberts of high-light brightness has been met. 

The general principle of reflective or Schmidt optics, as used in 
projection, has been described in several publications. 1 ' 2 In Fig. 4 
the essential features of it are shown. Here a thin aspherical lens 
placed at the center of curvature of a spherical mirror introduces an 



1948 



LARGE-SCREEN TELEVISION 



35 



amount of spherical aberration equal to that of the mirror but 
opposite in sign. 

The construction of the 42-inch mirrors (which was done at the 
RTA Camden plant) involved the development of a special machine 
shown in Fig. 5. This figure gives a general view of the grinder 
having a 53-inch turntable. A 42-inch mirror blank is being lowered 
into a cradle by an electric hoist operated by the author and an assist- 
ant. The weight of the blank is 350 pounds. A view of the polisher 




Fig. 7 Aluminizing equipment and finished 42-inch mirror. 

hi operation is shown in Fig. 6. With polishing completed the mirror 
was aluminized in the tank shown in Fig. 7. A mirror already alumi- 
nized can be seen at the left. Such large mirrors having relatively 
short focal lengths can produce weird optical effects such as shown 
in Fig. 8. 

The construction of aspherical correcting lenses has been done 
essentially by the methods described in cited publications. They 
were made of glass, an inherently costly process. Eventually, how- 
ever, these lenses may be molded from plastics just as in the case of 
correcting lenses for home-projection-television receivers. These 
lenses are being manufactured by the thousands at a cost of a few 



36 



MALOFF 



dollars each. One of the advantages of plastic lenses is that they are 
practically unbreakable. 







Fig. 8 Close-up of 42-inch mirror. 

ACKNOWLEDGMENTS 

The author acknowledges with thanks the able assistance of 
Messrs. R. F. Leuschner'and M. Di Lorenzo in the construction of the 
optical systems described. 

REFERENCES 

(1) I. G. Maloff and D. W. Epstein, "Reflective optics in projection tele- 
vision," Electronics, vol. 17, pp. 98-105; December, 1944. 

(2) D. W. Epstein and I. G. Maloff, "Projection television," /. Soc. Mot. 
Pict. Eng., vol. 44, pp. 443-456; June, 1945. 



Developments in Large-Screen 
Television* 



BY RALPH V. LITTLE, JR. 

RCA VICTOR DIVISION, RADIO CORPORATION OF AMERICA, CAMDEN, 
NEW JERSEY 



Summary An experimental large-screen program is being carried on to 
determine the requirement for theater use. The governing factors: the 
light source, the optical system, and the screen are discussed. Photographs 
show equipment built for an experimental program. 



THE HIGH DEGREE of excellence achieved in the production and 
reproduction of sound motion pictures has placed this art above 
all others in popularity and entertainment value. With high stand- 
ards already established, large-screen television makes its debut 
in the entertainment field, not as a competitor, but as an ally, an 
ally \vith mutual interest and, we believe, vast possibilities. 

Large-screen television is still in the experimental stage but con- 
siderable progress has been made during the past two years. Ex- 
perimental equipment has been built and demonstrated with ex- 
cellent results. This equipment, which will now be described, will 
form the basis for determining specific requirements and future design. 

There are three major elements in a large-screen projection system 
which are combined to produce the over-all result viewed on the 
screen. The first is the source of light and picture, the projectioy 
kinescope, which translates the video information into a pattern of 
light on the tube face by the scanning process; second, the optical 
system, the function of which is to collect the light rays from the 
face of the kinescope and direct them to the screen, properly focused, 
as an image of desired size; and third is the screen from which the 
picture is viewed. These three elements must each be designed for 
their best efficiencies in a co-ordinated system, in order to make 
possible the best in picture quality and brightness. We shall examine 
each element of such a system in order to understand their limita- 
tions and discuss the problems common to each. 

Presented October 23, 1947, at the SMPE Convention in New York. 

JULY, 1948 JOURNAL OF THE SMPE VOLUME 51 37 



38 



LITTLE 



July 



The projection kinescope is similar to that used in the direct- 
viewing table-model television receiver and requires the same video 
amplifier, deflection, and high-voltage functions as required for the 
receiver; the differences are those of magnitude in order to obtain 
the very bright picture required. We st?e in Fig. 1, the diagram of a 
typical projection kinescope tube; the electron gun here emits a 
stream of electrons which are focused by an electron lens and ac- 
celerated by the high-anode potential, which is 50 kilovolts for the 
7-inch tube, to the screen where it causes the phosphor coating of the 
face to emit light in accordance with the density of the electron beam 
which is controlled by the video signal. The deflection yoke sur- 
rounds the neck of the tube and is provided with suitable currents 



SECOND ANODE CONTACT 



CON "POL GMD 




1 Cross section of projection kinescope. 



to make the scanning raster necessary to form a picture-image pattern. 
Television has no satisfactory method of using a supplementary high- 
intensity light source, such as a carbon arc, which might be controlled 
At video frequencies; so high-light brightness is a function of phosphor 
efficiencies. The method then of obtaining high-light output from a 
projection kinescope, as compared with a home-receiver kinescope, 
is to provide high accelerating voltage on the tube. This permits the 
phosphor to be bombarded with electrons of high velocity which 
produces more light while the current remains low. 

The relative voltages used on typical kinescopes are : for the 10-inch 
home receiver, 9000 volts, while 50,000 volts is used for the 7-inch 
projection kinescope, and for the larger 12-inch and 15-inch projection 
kinescopes, 80,000 volts accelerating potential is used. Although 
the high voltages are used, the current requirements are small and 
are generated in safe radio-frequency power supplies which have very 



1948 



LARGE-SCREEN TELEVISION 



39 



lo\v stored energy. Future developments will be centered on the 
improvement of the phosphors and the electron optics of the kine- 
scope. The typical projection kinescope high-light brightness is 
about 3000 foot-lamberts. 

The second requirement of the projection system is the lens and 
since Mr. Maloff has discussed this subject in detail, only a brief sum- 
mary will be made. You are familiar with typical motion picture 
lens which may nominally be an //2.0 with a 5-inch focal length and 
uses elements 2 1 /z inches in diameter. A refractive lens of this type 
for a kinescope of 7-inch diameter would require a lens equal to the 
face diameter to gather sufficient light from the picture and in a 




Fig. 2 Block diagram of simplifier. 

practical design could not exceed a speed of //1.5. The //1.5 lens 
would have a gain of 1.75 over the conventional, thus leaving much 
to be desired in efficiency. Television engineers soon realized that 
the lens system was one place where more gain might be realized. 
The reflective optical system of the Radio Corporation of America 
was devised and gave effective speeds to //0.6 with the 42-inch mirror 
system which has been completed for use with a 15-inch kinescope 
to produce an 18- X 24-foot picture. The relative speed as com- 
pared with the //2.0 system would then be eleven times the gain in 
light, a truly remarkable increase. Reflective optical systems are 
characterized by short focal lengths which are necessary in order to 
produce the fastest lens speed or smallest / number. The projector 
for the 6- X 8-foot screen uses a 21-inch mirror, a 14-inch correction 



40 LITTLE July 

lens, a 7-inch projection kinescope, and has a throw distance of 15 
feet. The projector for the 18- X 24-foot picture uses a 42-inch mir- 
ror, a 36-inch lens, a 15-inch kinescope, and requires a throw distance 
of 40 feet. 

The screen then forms the final link in our over-all system and 
affords another opportunity to improve the gain in picture brightness. 
Consideration has been given to the various types of screens available. 
Experience obtained in our experimental work indicates that some 
form of directional-viewing screen gives the best compromise in high- 











Fig. 3 Rear quarter view of 6- X 8-foot screen 
projector. 

light brightness and viewing field. The beaded screen has given good 
results in this respect and is used with our demonstrations, but further 
development is in order. Developments in screens promise to permit 
greater gains and it is expected that gains as high as 3 may be obtain- 
able to the advantage of the over-all system. 

The Society of Motion Picture Engineers recommends an optimum 
screen brightness of 7 to 14 foot-lamberts. Television is approaching 
this requirement of the theater; developments under way will pro- 
vide a picture equivalent to the recommended standard of brightness. 

In Fig. 2 is a diagram of the essential elements of the large-screen 
projector, the projection kinescope, the RCA reflective optical system, 



1948 LARGE-SCREEN TELEVISION 41 

the video amplifier, which modulates the kinescope to produce the 
light and dark areas corresponding to the television-camera image, 
the deflection circuits to produce the synchronized scanning raster, 
the radio-frequency oscillator and rectifier to supply the 50 kilovolts, 
and the necessary power supplies. 

The projector for the 6- X 8-foot screen is shown in Fig. 3 and is a 
completely self-contained unit which operates from a video signal 




Fig. 4 Control panel. 

supplied from a coaxial cable or a television receiver. The unit 
measures 53 X 32 X 60 inches and weighs 1200 pounds and requires 
18 amperes at 115 volts 60-cycle alternating current or approximately 
2 kilowatts. The cabinet houses the optical barrel containing the 
RCA reflective optical system, the 7-inch projection kinescope, and a 
50-kilovolt high-voltage rectifier unit. Aligned on each side of the 
cabinet are the video amplifier, deflection units for vertical and hori- 
zontal scanning voltages, the radio-frequency oscillator which drives 
the high-voltage rectifier, and the necessary regulated power supplies. 
The control panel (Fig. 4) is located at the rear and has all operational 



42 



LITTLE 



July 



controls accessible. It is noteworthy that most of these controls 
would not be made available on a commercial design, but would be 
on the associated chassis units since frequent adjustment is not 
required. The required controls would be found consisting of the 
contrast, brightness, optical focus, and electrical focus. A photo- 
graph of the optical barrel is presented in Fig. 5 to show the mounting 
of the mirror, the bottom tank of which houses the high- voltage supply 




Fig. 5 Optical barrel showing mounting of 
mirror. 



and effectively shields it from radiating. This unit must be very 
rigid to hold the optical system in precise alignment. 

An interior view of the left side (Fig. 6) shows the orderly arrange- 
ment of the electrical equipment used. The left-hand panel is the 
synchronizing circuit panel, the major unit on the right is the de- 
flection chassis which drives the deflection yoke on the neck of the 
tube. The other chassis are direct-current power supplies. 

The other side (Fig. 7) shows the video amplifier on the right. 
The radio-frequency oscillator below it drives the high-voltage supply. 



1948 LARGE-SCREEN TELEVISION 43 

i 




Fig. 6 Left side of 6- X 8-foot projector showing chassis. 



m 



Fig. 7 Right side of 6- X 8-foot projector showing chassis. 



44 LITTLE July 

On the left we have a power supply for the units just described and a 
fuse panel for the protection circuits. 

A unique design feature of the projector is the high-voltage power 
supply, Fig. 8. As previously mentioned, it is driven from a power 
oscillator operating at 20 kilocycles. Energy at this frequency is fed 
to a step-up transformer which develops 25 kilovolts peak-to-peak 
alternating current, Avhich is then doubled in the special rectifier 




1 1 




Fig. 8 50-kilovolt rectifier. 

circuit to furnish the 50 kilovolts required. The figure shows the 
actual supply designed for this equipment, and its unique features 
include the self-contained filament transformers built into the socket 
of each -tube. 

A similar high-voltage rectifier is shown in Fig. 9, but with a 
quadrupler to supply the 80 kilovolts required for the projector using 
the 18- X 24-foot screen. Tne radio-frequency voltage generated 
in the coil is impressed on each rectifier tube. These tubes for direct 
current are in series so that four times the voltage is realized across 



1948 



LARGE-SCREEN TELEVISION 



45 



the output resistor and kinescope. These unique power supplies 
employ a circuit developed by O. H. Schade of the RCA Victor Divi 1 - 
sion, Harrison, and a mechanical arrangement devised by Fred G. 
Albin, recently of Camden Engineering and now at the Hollywood 
office. 




Fig. 9 80-kilovolt rectifier. 



Fig. 10 shows the projector built for the 42-inch optical system and 
is the largest unit of its kind ever attempted. It will throw an 18- 
X 24-foot picture on the screen from the face of a 15-inch kinescope. 
The mechanical and electrical problems were of great magnitude as 



46 



LITTLE 



was to be expected. Any resemblance of this unit to another nation- 
ally advertised product is purely coincidental. This unit represents 
the accumulation of many years of effort on the part of many engi- 
neers in the RCA Victor Division located at Camden, Harrison, and 
Lancaster, and the RCA Laboratories of Princeton. Credit is due 
them for their contribution to the over-all project as well as to F. G. 
Albin who co-ordinated the design of the equipment described hero. 




Fig. 10 Large theater projector for 18- X 24-foot screen 
using 42-inch mirror and 15-inch kinescope. 



ACKNOWLEDGMENTS 

In closing, I wish particularly to thank Mr. Earl Sponable of 
Twentieth Century-Fox for making available the equipment which 
we are demonstrating this evening. This equipment, together witli 
the larger projector, form a part of a co-operative venture in theater 
television which the Radio Corporation is making with Warner 
Brothers and Twentieth Century-Fox as recently announced to the 
press. 



DISCUSSION 

Note: Chairman Larsen requested that discussion on the two 
preceding papers be held until after the Large-Screen Television 
Demonstration. Therefore, the following discussion concerns both 
papers. 

MR. J. I. CRABTREE : Does the aspherical lens need cleaning very often? If so, 
being plastic, do you not impair the optical properties in cleaning it? 

MR. I. G. MALOFF: Not especially in the large-screen projector. If it is cleaned 
with the antistatic compound, we do not have to clean it very often. In the home- 
projection receiver, we make a hood that protects it from collecting dust. The 
normal cleaning with a soft cloth does not spoil it, because we use the hardest 
available plastic. 

DR. E. W. KELLOGG : I should imagine the audience might be interested if Mr. 
Maloff would give us the figures of the optical speed or effective / number that is 
attainable in the Schmidt system, and also the field size in degrees so that they 
might compare it with what is possible' with camera lenses or projection lenses. 

MR. MALOFF: The / number as such loses its meaning at, I would say, about 
//1. 4. So the best figure is the efficiency of the lens. By defining efficiency as the 
ratio of the number of lumens delivered to the screen, to the lumens produced by 
the tube, we arrive at a figure between 30 and 40 per cent with the reflective optics, 
with a very large magnification. The figures for the//2 lens, for the same magni- 
fication, run close to 4 or 5 per cent. I cannot tell you the field angles, offhand. 

CAPTAIN A. G. D. WEST: How many lumens do you project in this projector 
and how many do you expect to project in the new 42-inch mirror projector? 

MR. MALOFF: Suppose we turn the answers to your question around. The 
prewar projector gave us high-light brightness somewhere between 1 and 2 foot- 
lamberts. That brightness was found in a number of theaters around the country 
by the Committee on Screen Brightness of the Society of Motion Picture Engi- 
neers, which report was published around 1936 or 1937. The size of our screen in 
the New Yorker theater in 1940 was 15 X 20 feet. The screen gain was 2: By 
gain of a screen, we mean the ratio of brightness normal to the screen, to the inci- 
dent illumination ; that is, how many foot-lamberts' brightness are obtained for 1 
1'oot-candle illumination or 1 lumen per square foot. 

What we are doing now is this: We went to. a 15-inch tube and increased the 
area of the emitter four times, roughly. Then we increased the voltage some- 
what, and we used an aluminum-backed screen. Before the war we also used an 
aluminum-backed screen, but it was of an amorphous type, which did not have a 
mirror reflecting the light that was going back toward the gun. It was an absorber 
of that light. We put it on only to maintain the luminescent material at the 
second-anode voltage. There is such a phenomenon known as ''sticking" of the 
luminescent material. That means it does not quite reach the voltage put on the 
second anode, never rising above the "sticking potential." 

This gives us a gain of approximately eight times. There are a few other small 
gains, for example, in higher light output from the phosphor. 

This would give us, with a perfectly diffusing screen having a gain of 1, a net 
gain of four times the prewar screen brightness. 

We do not^pTopose to use, with theater television, screens that illuminate ceiling 

47 



48 DISCUSSION July 

and floor. We want the light to fall where the people are. Therefore, we propose 
to build screens that will throw the light only where the audience is. We have 
done this to a certain extent with the home projection receivers. We hope to do 
so with the theater projection receivers. The screen in the home projection re- 
ceiver has a gain of 6. I doubt if we can get that kind of gain for a theater, but we 
ought to be able to get a gain between 3 and 4, and we are working hard at it. 

CAPTAIN WEST: As to the answer about how many lumens, I believe the pre- 
war, that is, 1941, projector gave about 200 or 300 lumens. 

MB. MALOFF: On the New Yorker installation we ran close to 500 microamperes, 
average beam current. That gives us a peak, say, of 2 milliamperes. At 70 kilo- 
volts, it is 140 watts. Now, 140 watts at 2 candle power per watt gives you 280 
candle power. Assuming that we emit from the face of the cathode-ray tube ac- 
cording to Lambert's law, we multiply that by 3. That gives us somewhere in the 
neighborhood of 600 or 700 lumens. The same arithmetic applies again now, ex- 
cept that we are getting between 4 and 5 candle power per watt from the lumines- 
cent screen, this new aluminized screen. The new screen has mirror aluminum; 
it is not amorphous aluminum. We coat the screen with organic material. We 
fill all the little holes, the little depressions in the luminescent material, and the 
coating leaves a shiny surface. Then we evaporate aluminum on that shiny sur- 
face, and by baking and evacuating with pumps, we exhaust all the organic ma- 
terial. So we have left a shiny aluminum surface over the luminescent material. 
In this way we more than double the efficiency of the luminescent material. 

CAPTAIN WEST: That is our practice, of course. However, I think we expect 
to get 1000 lumens from our 40-inch projector. You remember I mentioned about 
Dr. Zworkin's being in Paris. After he returned from that visit, I heard that he 
was achieving 12,000 lumens and 40 foot-lamberts on that size screen. So that 
rather depressed Professor Fisher, who was working on the other system. 

I should have liked to bring a projector here to compare with the one used in the 
large-screen television demonstration, but it was not possible. However, in Lon- 
don we are projecting on a larger screen. It is very difficult to make a comparison, 
but, first of all, I should say my impressions of the picture are exceedingly good. 
My first impression is an impression of the color. It is a better color than we are 
having at the moment for a larger screen. I like the blue white and the bluish 
white in the home receiver. 

Second, there seems to be good interlacing, which we do not have at home. 
The contrast range was very good. Was the center part film transmission? 

MR. LITTLE: I believe certain portions of that program were from film. 

CAPTAIN WEST: The transmission of the British Broadcasting Corporation 
suffers from a good deal of shading. Generally speaking, I am very favorably 
impressed. I think it is a very good picture, indeed. 

DR. K. PESTRECOV : I think we need a committee on standardization of screen 
terminology. Recently we heard a report on screen-brightness measurements. 
At that time the ratio of foot-lamberts to foot-candles on the screen was called 
efficiency of the screen. As I remember, the efficiency would run from about 
50 per cent to about 90 per cent. I believe Mr. Maloff prefers the term "gain." 
If it is really the same quantity, then a gain of 2 would correspond, as was defined 
a day or two ago, to an efficiency of 200 per cent. That is the first question. 

Second, if television engineers can design a screen, or hope to design a screen, 



1948 LARGE-SCREEN BRIGHTNESS 49 

with a gain of 2, or an efficiency of 2'00 per cent, the screen also should be suitable 
for general motion picture projection. Perhaps, it will be a real advance so far 
as obtaining brighter pictures in general, because for theater television you are 
not inclined to use one screen and another screen for motion pictures. 

MR. MALOFF: The first question is on efficiency and gain. There has not 
been any standardization in that field, so far, except among ourselves. Television 
engineers have a clear distinction between the two terms. 

The one term, efficiency of the screen, is simply determined by putting a 
photometer on the other side and determining how much light at all angles gets 
through that screen. I am mostly talking about transmission screens, but the same 
applies to reflective screens. However, when we talk about gain, we measure 
this by comparing the light with what would come from a perfectly diffusing 
screen according to Lambert's law. We concentrate the returned light into a 
narrow pyramid, more or less. Horizontally it is wide. What we are trying to 
do is to get 60 degrees width from the screen, completely uniformly, with a sharp 
cutoff beyond that. Vertically, we are trying to get a 20-degree spread. 

Theoretically, you can get close to a gain of 12 if you collect light that went to 
various places before. However, you can never get efficiency of the screen of 
over 100 per cent, because you absorb some light. 

Before very long, we shall all have to get together and straighten out this 
matter, at least among us television engineers. Then we might have either con- 
version factors to translate to motion picture practice, or perhaps we can adopt 
the same terminology and the same definitions. Such is the case of resolution 
right now. When we talk about resolution in television, we say "500 lines." 
When an optical man looks at it, he will say it is only "250 lines," because we 
count every line, white and black, whereas he is counting only the black lines. 

As to the second question, whether such screens as we are using now in the 
television industry are suitable for motion picture projection, we have various 
reflective screens. One concern is putting in a reflective screen with a gain of 
just about 6. It was demonstrated in New York and in other cities. Screens 
with a gain of 12 were demonstrated. That particular screen, however, has too 
narrow a vertical angle, and they have put in one with a lower value of gain. 

So, all screens, both of the translucent type and the reflective type, could be 
used in theater projection of motion pictures. However, in some of the theaters 
the angles are so wide that you cannot use a directional screen; tha"t is, where 
there is a second and third balcony. That is why we could not use a very high- 
gain screen in the New Yorker theater before the war. 

In an auditorium like this one we should use a curved type of screen. There 
is an exhibit right outside the door of a curved screen, which definitely can give 
you a different directional distribution, vertically and horizontally. However, 
the problem is not so acute for the motion picture engineers as it is for television 
engineers. You start with such high values of light that you can waste it. If 
you can put a few extra seats here and there, you do so. The light goes down, 
but you still hold within your standard; that is, if it drops from 10 to 7 foot- 
lamberts, you do not mind that very much if you have a few extra seats. 

We barely reach sufficient brightness. We cannot waste it, and we might have 
to waste a, few seats in the theaters in order to show theater television. 

DR. PESTRECOV: Thank you, Mr. Maloff. I purposely meant to provoke 



50 DISCUSSION July 

the discussion, because I have had discussions with Mr. Maloff before, 
and I more or less knew what he was talking about when he mentioned 
the term "gain." However, I believe that perhaps many people here do not 
know that term. As a matter of fact, I did not know it about two years ago, 
and many people in the optical industry and the motion picture industry still do 
not know that term. The point is that you get gain when you narrow the angle of 
reflection; is that correct? 

MB. MALOFF: That is correct. 

DR. PESTRECOV: So, perhaps, it really might be better to employ that term, 
make it standard, and then we shall not talk so much about the efficiency of the 
screen. As to the committee that reported on the brightness of the screen, what 
the committee actually measured at that time was the brightness of the screen in a 
certain direction. They did not measure the total light reflected, 1 believe. Per- 
haps some time in the future we can introduce that term and really talk about gain 
of the screen. In this particular case probably it does not have much meaning, 
but when we start to talk about television screens in the motion picture industry, 
then we have to use that term, and I think it should be more or less explained. 
Maybe if you explain it when you write this paper for publication, I think it would 
be very useful; at least, we shall have a definite and authoritative reference. 

MR. LITTLE: Captain West might be able to answer a question on screens. 
In his paper he mentioned the lenticular screen which they were using in England, 
which gives a gain of 3. He also showed slides showing the distribution through- 
out the house, and that screen gave excellent coverage. Captain West, would you 
care to give us some explanation of the type of screen that you use? 

CAPTAIN WEST: We are not using that screen at the moment. The one I re- 
ferred to there under the heading of lenticular, which makes a large gain, was first 
demonstrated by Dr. Muller in Berlin at an exhibition. It consisted of a series of 
mirrors like a cat's eyes you see when you are driving on the road at night, looking 
out at you. It was very carefully arranged. I tested it very clearly on this tele- 
vision projector, which was similar to the one I illustrated on Tuesday night, of 
the pipe-shaped tube of the lens. I must say that if you were sitting at the end 
of the row and got out of your seat into^the gangway, the picture vanished; and 
when you went back into your seat, it appeared again. The idea is that all the 
light was reflected back into the seats, and not all over the theater. That amount 
of light was conserved. It was always very expensive to make and had to be 
tailored for every theater. 

There is an intermediate type of lenticular screen which we have been using. 
We have not used it so much as we wanted to, because of the shortage of metal and 
other materials. It is similar to what was described by Mr. Maloff for the home, 
except that it is a reflecting screen instead of a transparent one. I think that it 
corresponds to the screen in my diagram, which I referred to as a "stippled- metal 
screen." That gives a reflection factor right down the center of about 2 l /2to 3 times. 

One more question. I suppose you are getting a good show for one particular 
reason, in that it is all coming down from that little tower up there, is that right? 

MR. LITTLE: Yes, that is correct. The program came from the Empire State 
Building, but I might add that the proximity really causes a great deal of diffi- 
culty. Tonight, about twenty minutes after seven, I would have said tonight's 
show was not going on, because we had a great deal of interference which appar- 
ently was cross modulation in the receiver between frequency-modulation and 



1948 LARGE-SCREEN BRIGHTNESS 51 

television signals. We were very much discouraged about putting on the show 
Some of the difficulty you did see in the picture during the show was caused in the 
receiver and not in the projection equipment. It was unforeseen, I assure you, 
and normally that type of interference is not present. 

CAPTAIN WEST: That should please you very much, because we find that when 
everything goes wrong, before a demonstration, it is usually all right. 

There is one other thing I would like to mention which helps very much, in 
presentation of television on the screen. That is the sound. We are doing ex- 
periments in theaters now which in the last eight years have had a little disturb- 
ance around them, not fit for the public to enter; in fact, all the seats had been 
taken out, parts of the roof were down, and that sort of thing. The sound is very 
bad in our television presentation. The sound was very good here tonight. I 
am absolutely certain that if you get good sound you get a much better picture. 
MR. BEN SCHLANGER: If we can call this theater television a baby, I wonder if 
we are not making this baby run before it creeps. From what I can see, you are 
limited to a screen characteristic which throws the light back in a very narrow 
angle. Is it not better to take theater television and put it into shelters which are 
made for theater television? You are overstepping your bonds in trying to show 
television in existing theaters, where 50 per cent of the location will be inadequate 
and will not show the job off as well as it could be. The way you light the interior 
of the motion picture theater, there would be too much light in competition to the 
amount of light that you can get off the screen with television. 

MR. LITTLE : I hasten to point out the remark during the paper, that the pres- 
ent equipment is the basis of an experimental program. We do not know what 
form television theaters will take, or what form television programming will take. 
We do not know what form television equipment, as such, will take. We are just 
embarking on this field, and we hope to get the answers. We certainly do not 
know them and as manufacturers we do not propose to give the answers to the in- 
dustry. We are trying to help the industry find the answers. You gentlemen are 
part of the industry, and we expect the answers to come from you. We cannot 
give them. We can build you the equipment if you can tell us what you want. 
MR. SCHLANGER: All'the demonstrations and all the tests have been in existing 
theaters. It has never been given a really fair trial in a room that would really 
show it off the way it should. 

MR. LITTLE: Maybe those limitations are inherent, but we do not believe so. 
We are certainly looking for an answer. 

MR. R. B. AUSTRIAN: Mr. Maloff, in describing the screens and assigning the 
values to them which you did, I understood you to make a statement that there 
was no reason why they could not be used interchangeably for regular motion 
picture projection. Do I assume that the screens you worked with were non- 
porous; and if you had to perforate them for proper sound presentation as to be 
acceptable today, would that not change some of your reflection characteristics? 
MR. MALOFF: Yes, very definitely, if you use directional screens. By the 
time you perforate it, you probably lose part of the effect that you gain. Maybe 
your sound effect will not be as good as you would like to have it. I do not think 
a perforated screen is an important item, but the industry probably thinks differ- 
ently. If we perforate a directional screen, depending upon the percentage of 
the holes to the rest of the screen, we shall lose that much more light. 



Theater Engineering Conference 

Ventilating and Air Conditioning 



Motion Picture Theater 
Air Conditioning* 

BY DWIGHT D. KIMBALL 

CONSULTING ENGINEER, NEW YORK, NEW YORK 

Summary Air conditioning as now defined involves four basic ele- 
ments. These are a definite controlled temperature, the maintenance of the 
desirable relative humidity, a predetermined rate of air movement, and air 
filtration. In a properly installed air-conditioning system these elements 
can be predetermined and independently controlled, but temperature, 
humidity, and air movement must be controlled with a definite relation one to 
the other. 

BASICALLY modern air conditioning is but the ultimate develop- 
ment of ordinary ventilation. For example, the ventilating 
system installed in Carnegie Hall more than 50 years ago was made an 
air-conditioning system by adding to the existing ventilating system 
the necessary cooling equipment without changes in the fan equip- 
ment or duct system. 

The generally accepted standard of summer theater atmospheric 
conditions is 80 degrees on a day of 95 degrees outside temperature, 
50 per cent relative humidity, and approximately 12 to 15 feet per 
minute air movement within the seating area. An excessive relative 
humidity will more than anything else lessen the sensation of comfort 
of the occupants of the theater. 

The conditions as above stated should extend to every seat in the 
theater and should not be merely the average over the entire theater 
seating area. Herein lies the importance of correct air distribution. 

Seventy degrees inside of the theater with 95 degrees outside (a 
difference of 25 degrees) definitely may cause a serious shock to some 
people, especially the aged and those not in the best of health, and is a 
source of discomfiture to most people. Physiological tests have 
shown that a 12-degree difference between inside and outside temper- 
atures is the desirable maximum. 

* Presented October 24, 1947, at the SMPE Convention in New York. 
52 JULY, 1948 JOURNAL OF THE SMPE VOLUME 51 



AIR CONDITIONING 53 

Frequently it is asked when the air-conditioning industry will pro- 
duce new type of equipment that will substantially reduce the cost of 
theater air conditioning. There is little or nothing of this nature in 
sight at this tune. 

The next advance to be anticipated is a means of independently 
providing for dehumidification. At present dehumidification is 
effected by first lowering the temperature of the air supply, to a point 
lower than that actually required for the cooling of the theater in 
order to extract the necessary amount of moisture from the air sup- 
plied to the theater, then raising the temperature of the air upon leav- 
ing the cooling coils by the use of the auditorium return air by-pass or 
reheat steam coils to raise the temperature of the air to a point at 
which it may be admitted to the theater. 

Independent dehumidifying equipment is now available but it is 
expensive, space-consuming, and requires high-pressure steam or gas 
for the regeneration (or drying) of the moisture-absorbing material. 

The major features of a modern air-conditioning system are air 
supply and its distribution ; cooling equipment, such as refrigeration 
or well water; and treatment of secondary spaces, including the pro- 
jection room, lounges, toilets, foyer, and lobby. 

AIR SUPPLY 

The volume of air supply, as well as the capacity of the cooling 
plant, is determined by calculating the heat load. within the theater 
including transmission of heat from without through walls, floor, and 
roof; heat and moisture given off by the theater occupants, including 
standees; and electric load. 

This calculation is so made as to determine separately the sensible 
heat and the latent heat. With total internal sensible heat load 
determined, a temperature differential between the desired room tem- 
perature and the temperature of the air admitted to the theater is 
selected, this depending upon the rate of air movement desired, the 
height of the air-supply diffusers above the floor, and the distribution 
of the air diffusers. This temperature diffusion difference may vary 
from 12 to 18 degrees. 

Sometimes the resulting determination of the amount of the air 
supply to the auditorium will be found to be equivalent to 18 to 20 
cubic feet of air per minute per occupant. But this is not the final 
answer because not 100 per cent of the air supplied can be applied 
directly tp the benefit of the theater's occupants. Some of the air 



54 KIMBALL July 

supplied may short-circuit to the return air and exhaust outlets, some 
is lost through doors and otherwise, and more air than thus deter- 
mined is required to assure its distribution to all portions of the seating 
area. 

Over a period of years it has been proved definitely that the air 
supply to the theater proper should be not less than 24 cubic feet of 
air per minute per occupant. For a de-luxe installation 30 cubic feet of 
air per minute per occupant may well be provided. 

In determining the capacity of the main supply fan, the air filters, 
and heating and cooling coils, there must be added to the air to be 
supplied to the theater proper the amount of air which must be sup- 
plied to the lounges, foyer, lobby, and other parts of the theater. 

DISTRIBUTION OF AIR SUPPLY 

Quite as important as is the volume of air supplied to the theater 
is its distribution therein. This is determined by the number, size, 
and location of the air-supply diffusers which should be so determined 
as to, shall we say, spray the air over the entire occupied area of the 
theater, including the standee space, thus serving every person in the 
theater. In this matter the area under the balcony must not be neg- 
lected. Invariably the air should be admitted to the theater from the 
ceiling, and in the case of balcony houses also from the balcony soffit 
for the seating area under the balcony and the standee area. 

The ceiling cannot be designed for the exclusive benefit of the ceil- 
ing diffusers but the utilitarian value of the ceiling diffusers and the 
inherent limitations upon the location thereof must be taken into 
consideration in the design of the ceiling. Ceiling diffusers may take 
various forms. There are the old-style plaster plaques, lacking the 
desirable diffusing and induction effects, and not especially sightly. 
Now more generally used are Anemostats, Aerofuse, or similar dif- 
fusing outlets. This type of air-supply outlet has the very impor- 
tant merit of producing a secondary air movement. 

In determining the arrangement of the air distribution in a balcony 
theater the theater should be considered as divided into three zones. 

1. That portion of the orchestra floor in front of the balcony rail. 
- 2 The orchestra floor area under the balcony. 

3. The balcony. 

The air distribution should be so designed as to provide a direct 
supply of air and a withdrawal of return air in direct proportion to the 
number of occupants in each of these zones. (See Fig. l.\ 



1948 



AIR CONDITIONING 



55 



However small may be the seating and standee area beneath the 
balcony it is essential that a direct air supply and return air outlets be 
provided therefor. 

The temperature of the air supplied to the theater during the winter 
at no time should exceed 80 to 90 degrees. With a higher temper- 
ature of the air-supply, stratification of the theater temperature will 
become very serious and promote wasteful operation. There was 
once found an air supply of 100 degrees temperature, a ceiling temper- 
ature of 95 degrees, and a floor temperature of 54 degrees. All steam 
was shut off from the air-heating coils for 30*minutes while 40-degree 



RETURN 
FROM BALCONY 



Am SUPPLY To- 

LINDER BALCONY 
AREA 




GRILLE 



Fig. 1 Diagrammatic longitudinal section through theater. 



air was blown into the theater to eliminate the high-temperature air at 
the ceiling, then 75-degree air was blown in for 30 minutes and the 
floor temperature became 70 degrees. 

RETURN AIR 

It is the universal practice to design theater air-eonditioning sys- 
tems upon the assumption that 75 per cent of the amount of air sup- 
plied to the theater auditorium is returned to the fan room for recon- 
ditioning and return (with 25 per cent of outside air) to the theater. 

The supply of 25 per cent of outside air to the theater is desirable 
and adequate for the elimination of odors in the theater. 

A general distribution of the air-supply diffusers is essential to a 



56 KIMBALL July 

proper air distribution and equally essential is the general distribution 
of the return-air outlets within the theater. 

A general distribution of the air-supply diffusers, with the return- 
air outlets limited to a restricted area, or vice versa, invariably proves 
unsatisfactory, causing excessive temperatures and a sensation often 
described as "dead" in those portions of the seating areas which are 
neglected by either supply-air or return-air outlets. 

The most satisfactory and generally used means of withdrawing re- 
turn air from the theater is through standard mushroom outlets 
located under the seats-, usually communicating with return-air tun- 
nels under the floor. In the balcony either mushrooms or riser 
grilles may be used, these communicating with the balcony void from 
which the return air is drawn back to the fan room. 

FAN-ROOM EQUIPMENT 

The main fan room is the heart of the air-conditioning system. 
The fan-room equipment includes the main air-supply fan, its driving 
motor, heating coils, cooling coils, air niters, sheet-metal casings, and 
piping connections. 

The capacity of all of this equipment is determined by the total air 
supply required for the theater and accessory spaces. 

Main Supply Fan 

Assuming a theater designed for 1000 persons including standees, 
and an air supply of 24 cubic feet of air per minute per occupant, we 
have a base figure of 24,000 cubic feet of air per minute. To this 
must be added an amount of air equal to that which must be supplied 
to lounges, foyer, lobby, and other parts of the theater, from which 
spaces it is not customary to withdraw return air, some air to replace 
that which is lost through duct seams, and a small amount of air to 
assure a mild excess air pressure within the theater to counteract in- 
filtration through the doors. 

The finally determined capacity of the blower will be found to be 
about 30,000 to 32,000 cubic feet of air per minute. The total re- 
sistance, or static pressure, will be found to be I 1 /* to \ l /% inches. A 
motor of 15 horsepower will be required to drive the blower. 

To avoid noisy operation the blower should be so selected as to 
operate with an outlet velocity of about 1200 feet per minute, or under 
some favorable conditions up to 1400 feet per minute. 



1948 Am CONDITIONING 57 

The pulleys of the V-belt motor and fan drive should be of the vari- 
pitch type to make possible any desired correction of the blower speed. 
The V-belts should be 25 per cent greater in capacity than that of the 
motor for greater durability. 

HEATING AND COOLING COILS 

The heating and cooling coils should be selected upon the basis of an 
air velocity of approximately 500 feet per minute through the coils, 
which is the generally accepted standard. 

* Heating coils using low-pressure steam will usually be two rows of 
tubes in depth, assuming a proper utilization of the return air. In 
general practice the number of rows of tubes required in cooling coils 
when using well water of 50 degrees or less in temperature is four. 
With well water above 50 degrees and up to 54 degrees six rows of 
tubes usually are used. If the well water is somewhat above 54 de- 
grees eight rows of tubes are recommended. Additional rows of tubes 
serve no useful purpose in theater work. 

With a well-water supply of 54 degrees and above the relative 
humidity within the theater on hot and humid days, or with capacity 
audiences, cannot be maintained at a level of comfort, say at 50 per 
cent or at the very maximum 55 per cent, and one of the main purposes 
of the air-conditioning installation is then defeated. Under such 
conditions the installation of supplementary refrigeration equipment 
is desirable. In fact, a condition frequently is found where refriger- 
ation equipment may best be used to provide for all of the cooling. 

Direct expansion cooling coils through which the refrigerant, usu- 
ally Freon, is circulated through the cooling coils directly from the 
refrigerating plant will be discussed hereinafter. 

AIR FILTRATION 

Among the forms of air filters most generally used are dry-cell 
filters of the so-called "throw-away" type and similar types of wire- 
mesh air filters, the cells of which are dipped in an oil preparation and 
when dirty can be washed, redipped, and reused. 

The problem of maintaining the efficiency of these air filters is a 
troublesome one in either case. After long experience the author 
adopted the use of the ' 'throw-away" type of filter because in most 
cases the engineer or janitor may throw away and replace the dirt- 
loaded cells but would much more often neglect to remove, wash, im- 
merse in oil, and replace the washable cells. 



58 KIMBALL July 

At best the operator generally regards the air filters as a nuisance. 
One engineer even removed the air-filter cells completely so that they 
would not become dirty. 

The above types of air filters if allowed to remain in use until they 
become excessively loaded with dust and dirt may reduce the supply 
of air to the theater as much as 50 per cent. 

Also available are automatically operating oil-immersed air filters 
in which the air-filter cells are attached to traveling motor-operated 
chains designed automatically to immerse the filter cells in a bath of 
oil contained in a liquid tank at the base of the filter unit, thus elimi- 
nating the frequent replacement or washing of the filter cells. 

A much more efficient and desirable method of air filtration, but 
also much more expensive and space-consuming, is found in the elec- 
trostatic type of air-cleaning equipment, such as the Westinghouse 
Precipitron and the Raytheon Precipitator. 

Wherever space may be made available and the considerably 
greater cost of this electronic air cleaning is acceptable to the theater 
owner its use is highly desirable. All replacement or washing of filter 
cells is then eliminated. 

Assuming a theater air-conditioning system using 30,000 cubic feet 
of air per minute, the comparative cost of the different types of air 
filters mentioned above will be found to be about as follows: 

Dry-cell throw-away type $ 500.00 

Air-mat type 1400.00 

Oil-dipped reusable type 

2 inches thick 870.00 

4 inches thick 1170.00 

Automatic oil-immersed 2400.00 

Electronic or electrostatic . 5100.00 

Clean air is desirable not only from a health standpoint but also as 
a protection of the theater furnishings and decorations. 

FAN-ROOM LAYOUT 

As has been said the heart of the air-conditioning system is found in 
the main fan-room equipment. For the purpose of this discussion a 
plan of a typical fan room is shown in Fig. 2. Quite generally this 
space is found available at an elevated level at the front of the theater 
at one side of the screen platform. 

In the interest of minimum total cost of installation of the heating 



1948 



AIR CONDITIONING 



59 



and air-conditioning systems it is desirable that the boiler room and 
refrigerating machinery (or well-water pump) be located in the same 
general area but in the basement to shorten the interconnecting pip- 
ing lines. 

This arrangement of the fan-room equipment is designed to give 
access to each piece of equipment, including both sides of the heating 
and cooling coils. This last is important for the inspection and clean- 
ing of the coil tubes and for repairs thereto when necessary. 

INTAKE 



WEATHER PROOF LouvREb 

4 iNbECT SCREEN- 



RETURN AIR FLOOR GHATINO 
OVER RETURN AIR Due T FROM 
AUDITORIUM. DAMPER BELOW 



Two PART DAMPER- 



MINIMUM AREA AUTOMATICALLY 

OPENS i CLObt-3 WITH FAN MOIOK 

OPERATION 

MAXIMUM AREA FOR Ust DURING 

IN BETWEEN 5tAbONb MANUALLY 

OPERATED 



ACCESS DOOR 

RtTimN AIR BY PASS 
WITH AUTOMA 
DAMPER IN DUCT BELOW 




SUPPLY BLOWER 
MOUNTED ON VIBRATION 
ELIMINATORS 



AUDITORIUM WALL- 



Fig. 2 Typical plan of fan room. 

The outside inlet should be made of such a size as to admit an 
amount of air at 500 feet per minute velocity equal to the capacity of 
the blower so that 100 per cent of outside air may be utilized during 
the "in-between" . seasons when neither heating nor cooling is 
required. 

Back of the weatherproof louvers there is provided a -louver-type 
damper made in two sections. The smaller section is sized to admit 
the amount of outside air required during the cooling and heating 



60 KIMBALL July 

season. This so-called "minimum outside air damper" is automati- 
cally operated so as to open when the fan motor is started and close 
when this motor stops. 

The larger section of the outside-air-intake damper is manually 
operated and is to be opened only during the period of fan operation 
in the so-called "in-between" seasons. The use of this so-called 
"maximum outside-air damper" will be found helpful during spring 
and fall seasons to provide ventilation and some cooling effect in 
mild weather with a resulting saving in operation costs. 

A portion of the return air is admitted to the apparatus chamber 
between the outside-air intake and the air niters. The remainder of 
the return air is admitted into the fan chamber beyond the cooling 
coils to mix with the air which has passed through these coils to serve 
as a reheat medium to raise the temperature of the air coming off the 
cooling coils, which has been lowered to the point required for the 
elimination of moisture resulting in an air temperature too low for 
admission to the theater. A by-pass damper provided at this point 
should be controlled automatically to maintain the correct tempera- 
ture of the theater air supply. 

An important feature of this fan-room layout is the placing of the 
blower in such a way that the air may freely enter the fan inlet, espe- 
cially important in the case of a double-inlet fan to prevent an unbal- 
anced or a noisy fan. Free access to all fan-room equipment is essen- 
tial for inspection, cleaning, and repairs. 

Years ago it was a frequent practice to include in theater installa- 
tions an exhaust fan to remove the excess of outside air used. This 
practice has long since been discontinued as serving no useful purpose 
and involving an unnecessary cost. 

AIR STERILIZATION 

It was suggested that this paper should cover the subject of air 
sterilization but inasmuch as that problem will be described separately 
in other papers, the remarks thereon will be brief here. 

Two methods of sterilization have been brought to the author's 
attention : ultraviolet radiation and glycol-vapor treatment. 

That method which not only treats the air passing through the air- 
conditioning chamber but also carries the germicidal agent on into 
the theater and to the theater occupants would appear to be the more 
effective. 

Glycol equipment, which is now available, requires but a small space, 



1948 AIR CONDITIONING 61 

is relatively inexpensive to install and operate, is odorless, nontoxic, 
and is carried directly into the theater in the supply air stream. 

The ultraviolet ray equipment involves the placing of lamp units 
in the theater walls and a considerable amount of wiring. The author 
is not at this time persuaded of the merits of this system for theater work. 

So far as is known, no theater up to date has been provided with 
germicidal-air-treatment equipment but this subject does seem to be 
worthy of very serious consideration. 

PROJECTION-ROOM VENTILATION 

The ventilation of the projection room is governed by the rules of 
the National Board of Fire Underwriters and in New York City by 
certain provisions of the City's Building Laws. Some of these require- 
ments are confusing and indefinite and are not specific in an engineer- 
ing sense. Moreover, the situation is further confused by the varying 
interpretations given by different inspectors or engineers representing 
these Bureaus. 

Fig. 3 shows the author's standard plan of projection-room ventila- 
tion which appears to be acceptable to all authorities having jurisdic- 
tion thereon. 

The essential features are as follows: (a) a motor-driven exhaust 
fan with ducts to remove the heat from the projection machines, ex- 
hausting 50 to 100 cubic feet per minute from each machine; (6) a 
second exhaust fan to ventilate the projection room, the rewind room, 
the motor-generator room, and the toilet room. Twelve to 20 
changes of air per hour may desirably be exhausted from these rooms 
because of the heat released therein. A single fan may not be used to 
serve both of these purposes, nor may either of these fans serve to 
ventilate any other spaces. The discharge ducts from these two fans 
should be carried directly to out-of-doors. No code specifically states 
this but the author has had objections filed to the carrying of these 
discharge ducts through other theater spaces; (c) two outside air 
ducts directly from the roof (or upper part of the side walls) to serve 
the machine rooms and the rewind room (New York City Code) ; (d) 
film cabinets of a capacity of 50 pounds or more of film are required 
to be provided with a vent directly to the outside of the building. 

The rules of the National Board of Fire Underwriters specifically 
state that the " Ventilation of the projection-room area shall not be 
connected in any way with the ventilating or air-conditioning system 
serving other portions of the building." 1 ' 2 



62 



KlMBALL 

LOBBY 



July 



The real problem in treating the lobby is that of counteracting the 
wind blowing in through the outer doors which is sometimes found 
to be blowing on into the theater resulting in annoyance to those per- 
sons occupying the rear theater seats. 

The use of radiators in the lobby is generally unsatisfactory because 
a large amount of lobby radiation is required for which it is generally 




1948 



AIR CONDITIONING 



63 



found difficult to find space, the radiators are objectionable in appear- 
ance even when recessed and grilled, and there will be times when the 
cold air will blow through the lobby into the theater, and the radiation 
is not immediately responsive to sudden demands for heat, such as 
when the outer doors are opened. 

A more efficient means of heating the lobby, and with the same 
equipment supplying conditioned air thereto, is found in the extension 
to the lobby of a branch duct from the theater air-conditioning supply 
duct and interposing in this branch duct a booster air-heating coil and 



FAN MOUNTED ON 
PLATFORM PLATFORM 
SUSPENDED FROM 
SLABABOVE. 

BOOSTER FAN- 



5ERWCE 

ROOM 



(FROM CONDITIONED AlR 

\ SUPPLY Ducr 



-BOOSTER COIL 




E- F- G i H ARE TYPE 
R-ZOAoiTAiR OUTLETS, 



Fig. 4 Lobby heating and air conditioning. 

a small booster fan which will supply air to the lobby at a pressure 
sufficient to counteract the pressure of the air blowing in through the 
outer doors. By this method the lobby is evenly heated during the 
winter and air-conditioned during the summer. 

Fig. 4 shows a typical lobby treatment. The solid lines show the 
preferred method; dotted lines show an alternate method. 

Lobby temperature control, during the heating season, may be 
accomplished by a thermostat operating a modulating steam-control 
valve at the booster coil or face and by-pass dampers at the booster 
heating coil. 



64 KIMBALL July 

LOUNGES AND TOILET ROOMS 

All toilet rooms, whether or not having windows, should be provided 
with mechanical exhaust ventilation. Windows are generally kept 
closed during the cold weather but when opened they may serve to 
admit air which will blow the toilet-room odors into the theater. 

Inasmuch as the toilet rooms are generally entered from the 
lounges the general practice is to supply conditioned air to the lounges 
and to draw air from the lounges through louvers in the toilet-room 
doors into the toilet room from which it is exhausted as above stated. 

AUTOMATIC CONTROLS 

The operation of a theater-heating and air-conditioning system 
lacking automatic-control equipment involves an excessive amount of 
attention on the part of the operator and a degree of skill which is 
rarely available. 

Automatic temperature and humidity control greatly lessens the 
amount of attention required of the operator, automatically compen- 
sates for varying occupancy and weather conditions, and lessens oper- 
ating costs. Automatic control devices are delicate and should be 
the subject of an annual checkup by the manufacturer of the equip- 
ment used. 

A simple system of automatic control would include the following : 

For Winter Operation 

A master duct-type modulating thermostat having its bulb located 
in the stream of the outside-air supply. A submaster modulating 
room thermostat located in the theater to control automatic valves 
inserted in the steam connections to the air-heating coils. A modu- 
lating duct-type thermostat in the main fan discharge duct designed 
to prevent the supply of air to the theater at too low a temperature. 

For Summer Operation 

A proper relative humidity in the theater is of prime importance 
because it more directly affects the comfort of the theater patrons than 
does temperature. To control the relative humidity an automatic 
modulating humidostat is located in the return-air duct near the fan 
room to so control the operation of a modulating three-way water 
valve inserted hi the cold-water mains connecting to the cooling coils 
as to pass through the tubes of the air-cooling coils that amount of 



1948 AIK CONDITIONING 05 

cold water required to lower ' the temperature of the air passing 
through the cooling coils to the temperature required to extract by 
condensation on the coils all excess of moisture beyond that required 
to maintain the desired relative humidity in the theater. 

This may reduce the temperature of the theater air supply below 
the temperature at which it may be discharged into the theater. 

Then a portion of the return air is carried around the cooling coils, 
thus utilizing the heat picked up in the theater for the raising of the 
temperature of the air supplied to the theater. An automatic damper 
is provided in this return-air by-pass controlled by the submaster 
modulating room thermostat described under " winter operation." 

A manually operated summer-winter switch is provided to transfer 
the effect of the submaster room thermostat from the control of the 
steam valves at the air-heating coils during the heating season to the 
control of the automatic return-air by-pass- damper during the cooling 
season. This switch also holds the three-way water valve closed dur- 
ing the heating season and the steam valves closed during the cooling 
season. 

A simple means of opening and closing the minimum outside-air- 
intake damper when the main supply fan is started and stopped is 
desirable. This consists of a damper motor applied to the minimum 
intake damper and an electric-pneumatic switch wired into the motor 
circuit with a damper motor. * 

A lobby thermostat of the modulating type with an automatic 
valve in the steam connection to the lobby booster heating coil is 
essential to the control of the lobby temperature. The usual chrono- 
therm is assumed to be provided for the control of the heating-boiler 
oil burner. 

This system may be elaborated upon at will. It will include a small 
air compressor and other incidental equipment. An electrical auto- 
matic control system may be installed to accomplish the same ends. 

It will be noted that reference is made above to the use of modulat- 
ing thermostats. These may be used for heating controls only where 
a vacuum steam-heating system is installed. Such a system is highly 
desirable because it provides for the only successful method of control- 
ling the temperature of the air supplied to the theater by making 
possible the modulation of the supply of steam to the air-heating coils 
in exact proportion to the demand for heat. 

A vacuum steam-heating system is more economical in operation 
than is a gravity-heating system and a substantial portion of the cost 



66 KIMBALL July 

of the vacuum-pump installation may be saved through a reduction in 
steam- and return-piping sizes and a saving in the cost of pipe covering. 

PRIMARY COOLING MEDIUM 
Well Water 

Where well water is obtainable at temperatures of 50 to 54 degrees 
it will serve every purpose required of air conditioning and the well 
and pump installation will cost but 20 to 40 per cent of the cost of the 
required refrigeration installation. 

If the well water is found to be above 54 degrees in temperature 
either supplementary refrigeration equipment must be provided or a 
higher relative humidity will occur in the theater with a sacrifice in 
comfort conditions. 

Refrigeration 

The capacity of the necessary refrigeration installation is deter- 
mined by generally understood if rather involved calculations. An 
ample capacity in the refrigeration plant is a very comforting and 
reassuring thing. 

It has been the author's experience, including a survey of 100 
theaters for one chain, that a general checking figure on the tonnage 
of refrigeration required will run about as'follows: 

600-seat theater .12 occupants per ton 

1000-seat theater 14 occupants per ton 

1500-seat theater 15 occupants per ton 

1800-seat theater 16 occupants per ton 

Larger theater 17 occupants per ton 

Generally, Freon is the refrigerant used ina ir-conditioning work. 

The refrigeration plant will include one or two compressors as re- 
quired; motor; means of condensing, i. e., the cooling of the com- 
pressed refrigerant; water chiller, a chilled-water circulating pump, 
and a chilled-water circulating piping system, if a water-circulating 
system is required or .used; and starters, automatic controls, and 
other parts. 

A single compressor may be installed if the tonnage is 50 tons or less 
or if a centrifugal compressor is used. Interruptions of service are 
very rare. Reciprocating compressors are very generally used, 
especially in theaters of 1500 seats or less; a centrifugal compressor 
may well be used for larger theaters. 



1948 AIR CONDITIONING 67 

The motor horsepower per ton of refrigeration will vary with the 
actual operating conditions and motors of ample capacity which will 
not become heated under maximum load conditions should be se- 
lected. Generally speaking the motor capacity should be not lesS 
than one and one tenth to one and two tenths horsepower per ton, or 
slightly less sometimes with very cold condensing water. 

Condensing, or cooling of the compressed refrigerant coming from 
the compressor, may be accomplished by means of a standard shell 
and tube condenser supplied with water from the street mains, from a 
cooling tower, or by an evaporative condenser. 

If the street water may be used the least cost of installation results. 
In New York City the supply of city water for this purpose is limited 
to 2,680,000 gallons of water per year and this is not sufficient for even 
a 600-seat theater. Then a cooling tower must be used to provide 
condensing water for a shell and tube condenser, or an evaporative 
.condenser may be used instead of the shell and tube condenser and 
cooling tower except in some cases an evaporative condenser cannot be 
installed within restrictions of the New York City refrigeration code. 

Where the indirect, or water-circulating system must be used, as in 
New York City, a shell and tube water chiller, similar in construction 
to the condenser, must be used with a chilled-water circulating pump. 

Automatic high- and low-temperature controls, a low- temperature 
compressor cutout to prevent freezing of the water in the chiller, and 
usually compressor capacity controls are applied to the water chiller. 

The well-water or chilled-water piping carrying the cooling water 
to and from the cooling coils must be insulated with molded cork, 
preferably 2 inches thick. An alternate to this indirect, or water- 
circulating, system is the direct expansion' system in which the 
compressed refrigerant after being condensed or cooled in the con- 
denser is conveyed directly to and from the cooling coils. 

This direct expansion system is less expensive to install because it 
eliminates the water chiller and water-circulating pump and reduces 
insulation costs. However, it cannot be installed in places of public 
assembly in New York and certain other cities. 

Where the main fan room with the air-cooling coils is located at a 
considerable elevation above the compressors the direct expansion 
system operates at a disadvantage, and there is a further disadvantage 
in the direct expansion system in that it does not lend itself to a satis- 
factory method of the automatic control of theater temperature and 
humidity. 



68 . KIMBALL k July 

NOISE 

Sometimes a small matter can be the cause of very objectionable noise 
and still be difficult to locate. The most frequently found causes of 
noise might be listed in the following order of frequency of occurrence : 

1. Lightly constructed duct work having poorly made seams and 
joints, insufficient bracing permitting the vibration of the duct sheets, 
bad turns, loose dampers, and edges of metal projecting into the ducts. 

2. Excessive air velocities through the ducts or through the supply 
grilles and diffusers. Maximum duct velocities should not exceed 
1200 feet per minute at the fan, or possibly 1400 feet under favorable 
conditions, the air velocity being gradually reduced as branches are 
taken from the main duct to about 600 feet in the individual branches. 

3. The blower is by no means the most frequent source of noise 
although usually first suspected. An excessive fan speed or an exces- 
sive air velocity through the fan outlet will cause noise. The correct 
blower speed will depend upon the size, type, and characteristics of the 
blower. The air-outlet velocity from the blower should not be over 
1400 feet per minute and 1200 or 1300 feet is better. No sharp bend 
in the duct w r ork should be made near the blower outlet. The blower 
must be reasonably free from vibration. It must be so placed that 
the distance from the blower inlet ring to the enclosing wall should be 
approximately equal to the diameter of the fan inlet. This is espe- 
cially important in the case of a double-inlet, double- width blower. A 
canvas sleeve must be provided in duct connections to blowers so 
that blower vibration wilfnot cause a vibration of the ducts. A loose 
belt can cause much noise in itself and cause the blower to become 
noisy. A blower wheel out of balance or with loose shaft collars may 
cause pounding. 

4. A motor is sometimes noisy, perhaps because of faulty setting 
or even due to its construction. The motor may have to be replaced 
by a quiet motor. 

If the noise is caused by air travel in or out of the fan the simplest 
cure may be the installation of acoustical duct lining for a distance of 
about twenty feet. 

MAINTENANCE 

The installation of an air-conditioning system involves a very sub- 
stantial investment of money and includes much equipment. Most 
assuredly it is worthy of the utmost care. Neglect of this equipment 
temporarily may save money but ultimately it will involve an expense 
largely exceeding the amount saved in failing to maintain the 



1948 AIK CONDITIONING 69 

equipment properly. Moreover failure to maintain the equipment 
properly in good condition inevitably will increase the operating costs. 

COSTS 

The costs of an air-conditioning installation will vary so widely with 
the type of installation involved that no general figures may be given. 

Prices have been changing so rapidly that it is difficult to keep up to 
date on them. In 1942 bids were received on a theater air-condition- 
ing installation which was not made* because of war restrictions. 
Last month new bids were received upon the same plans and specifica- 
tions. The new bids exceeded those of 1942 by 78 per cent. At least 
half of this increase appears to have occurred within the last two years. 

GUARANTEES 

Do not buy air-conditioning systems upon the basis of guaranteed 
theater conditions. Proving the facts in court is almost impossible. 

The standard guarantee of results is that a condition of 80 degrees 
and 50 per cent relative humidity shall be maintained within the thea- 
ter when an outside temperature of 95 degrees dry bulb and 75 degrees 
wet bulb prevails, with a 100 per cent occupancy of the theater, and 
while using a predetermined volume of outside air. In thirty years 
the author has yet to see these conditions simultaneously prevailing 
for such a test. 

CONCLUSION 

In the foregoing it has been possible to give but a bare outline of a 
theater air-conditioning system. Actually such an installation in- 
volves a multitude of details, all of which are important, many of 
which are highly technical, and all of which must be correlated care- 
fully. To prove successful it must be a compound of theory and prac- 
tical experience, with the latter predominating. 

It has been said that he who serves as his own lawyer has a fool for a 
client. Looking back over many years of experience in theater air 
conditioning it seems that much the same thing may be said of one 
who assumes to act as his own engineer in the installation of an air- 
conditioning system. Competent advice will save the purchaser a 
great deal of worry . 

REFERENCES 

(1) A. C. Dowries, "Gases from carbon arcs," /. Soc. Mot. PicL Eng., vol. 35, 
pp. 32-47; July, 1940. 

(2) P. Drinker and J. R. Snell, "Ventilation of motion picture booths," /. Ind. 
Hyg. and Tox., vol. 20, p. 321; April, 1938. 



Theater Engineering Conference 

Ventilating and Air Conditioning 



Air Purification by Glycol Vapor 

BY J. W. SPISELMAN 

Am PURIFICATION SERVICE, INC., NEWARK, NEW JERSEY 



Summary The germicidal activity of glycol vapor on air-suspended bac- 
teria and viruses has been clearly demonstrated. The most suitable com- 
pound thus far found for use in such air disinfection is triethylene glycol. 
When dispersed in air as a true vapor in exceedingly small amounts it is 
highly germicidal for pathogens of the respiratory tract, including influenza 
virus. It is nontoxic, nonirritating, odorless, tasteless, invisible, and inex- 
pensive. Satisfactory devices for the vaporization and regulation of bacteri- 
cidal concentrations of glycol are now made and are in use. 

DURING THE LAST fifty years great strides have been made in 
protecting our people from the spread of disease through the 
food we eat and the liquids we drink. Our water and milk supplies 
are guarded with unceasing vigilance ; our foods and our drugs must 
meet tests of purity laid down in a rigid code. 

But what about the air we breathe? 

A man eats about two pounds of food a day. He drinks, say, a 
quart of liquids a day. But he breathes about 80 pounds of air per 
day. That air contains germs, dusts, smoke, organic matter, pollen, 
and noxious gases. 

Man has through evolution and environment built up his ability 
to withstand the onslaughts of these air-borne enemies; but that line 
of defense is vulnerable, and is often beaten down. In fact, it has 
been established that better than 50 per cent of all industrial sickness 
absences are due to respiratory diseases. 1 And these respiratory 
diseases are due primarily to air-borne infection! 

And the questions are quite properly asked "What can be done 
about it? What can be done to sanitize, or disinfect, or sterilize the 
air which is being continuously contaminated with bacteria and 
viruses dispersed into it as people around us cough, sneeze, or talk? 

* Presented October 24, 1947, at the SMPE Convention in New York. 
70 JULY, 1948 JOURNAL OF THE SMPE VOLUME 51 



AIR PURIFICATION BY GLYCOL VAPOR 71 

What can be done to protect us when we are congregrated in places of 
public assembly, theaters, schools, and industry?" 

This paper presents a picture showing how far one branch of air 
sterilization has gone toward answering those questions. 

Early in 1941, Drs. Robertson, Bigg, Miller, and Baker of the 
University of Chicago announced 2 that they had succeeded in steri- 
lizing air by using certain glycols. They used propylene glycol, one 
of a family of glycols, and obtained almost instantaneous sterilization 
of the air in a test chamber infected with high concentrations of staph- 
ylococcus and streptococcus germs. 

In the latter part of 1941 just before the United States entered the 
war, while selective-service camps were expanding, the Surgeon 
General of the Army formed the Commission on Prevention of Air- 
borne Infection and Control of Influenza and appointed the same 
Dr. Robertson as chairman. Because of the extensive experience 
The Research Corporation had acquired during the preceding years in 
glycol air conditioning, the Corporation was asked to assign the 
group, which now comprises Air Purification Service, Inc., to assist 
Dr. Robertson's Commission in various phases of further develop- 
ment and engineering. 

The development since that early period has been extensive. At 
the very beginning, it became apparent that it was not the fine mist 
of glycol that was the active agent but it was the true gaseous vapor 
of the glycol. 3 ' 4 For the vast majority of cases triethylene glycol 
rather than propylene glycol was more economical and efficient. 5 
Equipment was developed for the true vaporization of the glycols, 6 
and extensive field tests were performed. 7 

It also became apparent that the amount of triethylene glycol 
necessary for such sterilization was fantastically minute. One cubic 
centimeter of glycol liquid would sterilize 250 to 400 million cubic 
centimeters of air. Visualizing it in another manner, all the air in a 
building covering a full city block and six stories high could be steri- 
lized by one pint of triethylene glycol. An air-conditioning system 
using 15,000 cubic feet per minute of fresh air would require only 
five ounces of triethylene glycol per hour for sterilization. The 
actual quantity of vapor in the air approaches that of our most rare 
gases; it is less than Vioo the quantity of neon in the air we breathe. 

What are these glycols? Chemically they are kin to the alcohols; 
physically they look quite like glycerin. Triethelyne glycol (TEG) 
is a mildly viscous, colorless, and odorless liquid which, when vaporized, 



74 



SPISELMAN 



July 



It should be remembered that 
at the stage of our present knowl- 
edge, glycol vapor definitely had 
been shown to be a preventive 
medium, but not a cure, for air- 
borne infection. Yet, recent work 
in the aerosol field has indicated 
that the glycols may also have 
a therapeutic value by forming 
antibiotics with the blood 
serum. 12 ' 13 This work undoubt- 
edly will be followed up for 
further knowledge on this point. 

Glycol is vaporized through 
the medium of heat and a pre- 
heated stream of air. Triethyl- 
ene glycol for instance, cannot 





Fig. 2 Typical installation of 
vaporizer. 



Fig. 1 Vaporizer. 

be simply boiled to vaporize it, 
since it boils at 550 degrees 
Fahrenheit, but starts to decom- 
pose chemically at approximately 
300 degrees Fahrenheit. The 
equipment for such vaporizing 
is not complex; present equip- 
ment available is foolproof, eco- 
nomical of operation, and small 
for the job it can do. The 
present full-size glycol vaporizer 
has a base of 15 X 15 inches 
and is but 18 inches high, and 
will treat 20,000 cubic feet per 
minute of fresh air. 

Its application to an air-con- 
ditioning or ventilating system 
is generally mechanically simple 
after the proper engineering con- 
siderations have been made. A 
small quantity of air, roughly 
about 20 cubic feet per minute, 
is continuously preheated within 
the vaporizer to the proper 



1948 



AIR PURIFICATION BY GLYCOL VAPOR 



75 



vaporizing temperature under close thermostatic control, and is then 
induced over evaporating surfaces containing heated TEG. This 
carrier stream, warm and laden with glycol vapor, is then injected 
into the main stream of air in the ventilating system. The glycol 
disseminates within that main stream and is thus carried through 
the distributing ducts throughout the ventilated area. .Complete 
permeation of every nook and cranny of the treated space is thus 
obtained. 




Fig. 3 Installation within a plenum 
chamber. 



Fig. 4 Installation across a heating 
coil. 



Figs. 1 to 5 show the glycol-vaporizing unit and typical examples of 
applications to air systems. 

Fig. 1 shows the vaporizer itself. A small stream of air enters the 
top left-hand inlet, is preheated under thermostatic control, flows over 
evaporating surfaces and an indicating thermometer, thence out 
through the outlet port on the top right hand.. The output is based 
on the temperature of the leaving air and is a logarithmic relationship. 
The bottom of the vaporizer is a tank section holding five gallons of 
glycol. There are no moving parts in the unit. 






76 



SPISELMAN 



July 



Fig. 2 shows a typical installation. The vaporizer is set conven- 
iently close to the suction side of the main blower of a ventilating or 
air-conditioning system. The small stream of air is induced through 
the glycol-vaporizing unit by the suction of the main blower, and the 
glycol-vapor-laden output stream flows directly to the blower to be 
distributed throughout the system. 




Fig. 5 Size of unit. 

Fig. 3 shows another type of installation in which the glycol vapor- 
izer is placed within a plenum chamber on the suction side of a blower. 
Here the difference in pressure between the outside of the plenum 
and inside is used to induce the small stream of air through the 
vaporizer. 

Fig. 4 shows the unit operating by obtaining the necessary small 
pressure drop by means of the pressure drop of a coil in the venti- 
lating system. The pressure drop across the heating coil in this case 
is sufficient to force the air through the vaporizer to insure proper 
operation. 



1948 AIR PURIFICATION BY GLYCOL VAPOR 77 

Fig. 5 shows an installation similar to Fig. 2 and indicates the 
relative size of the unit in the far background as compared to other 
component parts of a ventilating system. 

In all cases, the glycol-vaporizing unit is interlocked with the blower 
motor, so that when the blower is shut down, the heating elements 
of the vaporizer are also shut off and the vaporizer becomes inactive. 

The cost of TEG is relatively low; a 1000-seat theater will use 
about eight cents worth of TEG per hour of operation. The electrical 
power required for the vaporizer is less than 750 watts, and would be 
lost in the total electrical bill of such a house. An illustration of such 
an installation in a large theater is in the Rivoli Theater, New York 
City. With the close co-operation of Mr. G. P. Skouras and Mr. 
Montague Salmon, managing director, operation costs and public re- 
action are being carefully noted. 

One of the results noted in a glycolized atomsphere is the feeling of 
"freshness" which seems to pervade the air. The mustiness often 
associated with air-conditioning systems is eliminated. Our ex- 
planation for that is that the molds and similar organisms which will 
collect in duct work and give off odors in their life processes are killed 
by the glycol vapors, and the odor disappears. 14 We believe also 
that there is some control over odors generated in an occupied area. 

In closing, it should be borne in mind that when a vapor is used 
for the control of air-borne bacteria and viruses, it pervades the entire 
atmosphere. It is where you want it when you want it at the source 
of such contaminating organisms, the mouths and nostrils of all of us. 

REFERENCES 

(1) William M. Gafafer, "Manual of Industrial Hygiene," United States 
Public Health Service, 1943. 

(2) O. H. Robertson, E. Bigg, B. F. Miller, and T. Baker, "Sterilization of 
air by certain glycols employed as aerosols," Science, vol. 93, no. 2409, pp. 213- 
214; February, 1941. 

(3) O. H. Robertson, "Sterilization of air with glycol vapors," The Harvey 
Lectures Series, vol. 38, pp. 227-254; 1942-1943. 

(4) O. H. Robertson, B. F. Miller, and E. Bigg, "Method of Sterilizing Air," 
United States Patent No. 2,333,124, November 2, 1943. 

(5) M. Hamburger, T. T. Puck, and O. H. Robertson, "The effect of tri- 
ethylene glycol vapor on air-borne beta hemolytic streptococci in hospital wards 1," 
J. Infect. Dis., vol. 76, p. 208; May, 1945. 

(6) S. C. Coey and J. W. Spiselman, "Space Sterilization," United States 
Patent No. 2,344,536, March, 1944. 



78 SPISELMAN 

(7) O. H. Robertson, "New methods for the control of airborne infection 
with especial reference to the use of triethylene glycol vapor," Wisconsin Med. J., 
vol. 46, p. 311; March, 1947. 

(8) O. H. Robertson, "Disinfection of air bygermicidal vapors and mists," 
Amer. J. Pub. Health, vol. 36, pp. 390-391; March, 1946. 

(9) O. H. Robertson and T. T. Puck, "The lethal effect of triethylene glycol 
vapor on air-borne bacteria and influenza virus," Science, vol. 97, p. 142; Feb- 
ruary, 1943. 

(10) T. M. Harris and J. Stokes, Jr., "Airborne cross infection in the case of 
the common cold a further clinical study of the use of glycol vapor for air sterili- 
zation," Amer. J. Med. Sri., vol. 206, pp. 631-636; April, 1943. 

(11) T. M. Harris and J. Stokes, Jr., "Summary of a three-year study of the 
clinical applications of the disinfection of air by glycol vapor," Amer. J. Med. Sci., 
vol. 209, p. 152; February, 1945. 

(12) S. J. Prigal, T. H. McGavack, F. D. Speer, and O. R. Harris, "Aerosol 
penicillin," /. Amer. Med. Ass., vol. 134, pp. 938; May, 1947. 

(13) S. J. Prigal, T. H. McGavack, and M. Bell, "The effect of propylene 
glycol on the antibiotic activity of human serum," Amer. J. Med., vol. 3, p. 185; 
August, 1947. 

(14) M. Mellody and E. Bigg, "The fungicidal action of triethylene glycol," 
/. Infec. Dis., vol. 79, pp. 45-56; July, 1946. 



FORTY YEARS AGO 

How Moving Pictures Originated 

A paragraph is going the rounds of the press giving the following ver- 
sion of the origin of moving pictures : 

Sir John Herschel after dinner in 1826 asked his friend, Charles Bab- 
bage, how he would show both sides of a shilling at once. Babbage re- 
plied by taking a shilling from his pocket and holding it to a mirror. 
This did not satisfy Sir John, who set the shilling spinning upon the 
dinner table, at the same time pointing out that if the eye is placed on a 
level with the rotating coin both sides can be seen at once. Babbage was 
so struck by the experiment that the next day he described it to a friend, 
Dr. Fitton, who immediately made a working model. On one side of a 
disk was drawn a bird, on the other side an empty bird cage; when the 
card was revolved on a silk thread the bird appeared to be in the cage. 
This model showed the persistence of vision upon which all moving 
pictures depend for their effect. The eye retains the image of the ob- 
ject seen for a fraction of a second after the object has been removed. 
This model was called the thaumatrope. Next came the zoetrope, or 
wheel of life. A cylinder was perforated with a series of slots and 
within the cylinder was placed a band of drawings of dancing men. On 
the apparatus being slowly rotated, the figures seen through the slots 
appeared to be in motion. The first systematic photographs taken at 
regular intervals of men and animals were made by Muybridge in 1877. 

The Moving Picture World, April 4,1908 



Theater Engineering Conference 

Ventilating and Air Conditioning 



Ultraviolet Air Disinfection 
in the Theater* 

BY L. J. BUTTOLPH 

GENERAL ELECTRIC COMPANY, NELA PARK, CLEVELAND, OHIO 



Summary Theater attendance, and the decrease during times of epi- 
demic respiratory disease, involves a public-health and a theater-operation 
problem possible of partial solution by an increase in ventilation, a sanitary 
ventilation, probably effective only when provided in amounts physically and 
economically impractical because of the power and duct capacity required to 
heat and distribute outdoor winter make-up air. Ultraviolet air disinfection 
provides a way of making the air in the upper third or half of theater auditoria 
and accessory rooms as good as outdoor air, or a sanitary ventilation of the 
lower air, equivalent to 50 to 100 air changes, resulting fr6m the usual random 
vertical air circulation throughout the horizontal cross section of occupied 
rooms. Any sanitary ventilation value in the make-up air of a duct-heating 
and air-conditioning system, may also be increased five- to tenfold by using 
ultraviolet energy to disinfect all recirculated air to the bacterial equivalence 
of outdoor air. There are tabulated lamp requirements for upper-air and 
duct-air disinfection and schematic installation sketches. 

ANNUAL NEWSPAPER notices urging people to stay away from 
crowds during times of epidemic respiratory disease call atten- 
tion to the public-health problem of the motion picture theater. 
Those who stay away may be benefited but the resulting decrease in 
attendance is usually only enough to create an economic problem for 
the theater operator without solving his health problem. 

The only solution of this problem is basically one of ventilation, of 
providing about ten times as much air volume per patron, or ten times 
more air changes per minute or hour, than has been provided in the 
past. Optical considerations of screen-viewing distance and angle, to 
say nothing of the economics of building construction, make any 
radical increase from the current practice of about seven square feet of 
the floor area per patron out of the question. The alternative is that 

* Presented October 24, 1947, at the SMPE Convention in New York. 

JULY, 1948 JOURNAL OF THE SMPE VOLUME 51 79 



80 BUTTOLPH July 

of providing a greatly increased ventilation, a sanitary ventilation, in 
contrast with the minimum past practice found essential for the dilu- 
tion of body odors and the distribution of heat. In the northern half 
of the United States, the heating of much more oudoor air than is 
essential for the removal of the body heat of the theater patrons is 
economically impractical. 

The recently available process of ultraviolet air disinfection has 
neatly solved the whole problem of sanitary ventilation directly in the 
theater auditorium itself by providing throughout the whole upper 
half or two thirds of the theater auditorium and the accessory rooms, 
reservoirs of air as relatively free of disease-producing bacteria as is the 
outdoor air brought into the theater by mechanical means. Recently 
available air-sampling techniques 1 - 2 have demonstrated that in any 
occupied theater auditorium properly equipped with germicidal lamps, 
the internal air circulation induced by the ventilating system and by 
the body heat of the patrons is such as to provide at the breathing level 
a sanitary ventilation from the disinfected zone above, equivalent tc 
one to two air changes per minute or 50 to 100 air overturns per hour, 
in contrast with the five to ten practical by the mechanical introduc- 
tion of fresh air. 

To whatever extent there may be recirculation of air by the theater- 
heating or air-conditioning system there is a similar reason for in- 
stalling germicidal lamps in the air ducts to make the recirculated air 
equivalent to outdoor air for sanitary ventilation. In so far as any 
sanitary ventilating value may be attributed to the make-up air of the 
usual air-conditioning system, that value can thus be increased five- tc 
tenfold. 

A detailed discussion of the unique germicidal effectiveness of the 
2400- to 2800-angstrom wavelength of ultraviolet energy 3 " 7 is beyond 
the scope of this paper. Apparently, however, because the peak of the 
absorption curve of the nuclear protein of bacterial organisms occurs 
at a wavelength of about 2600 angstrom units, the resonance radiation 
of electrically activated mercury vapor, wavelength 2537 angstrom 
units, is, as has recently been pointed out by McDonald, 8 "the most 
lethal wavelength yet discovered. It is hundreds of times more lethal 
to cells than high-voltage X rays. ..." Also Luckiesh 9 has shown the 
same energy to be hundreds and even thousands of times more lethal 
than the ultraviolet and visible radiation in direct sunlight. It is for 
this reason that it is possible to disinfect air with intensities and total 
amounts of germicidal ultraviolet entirely practical to produce and 



1948 



ULTRAVIOLET AIR DISINFECTION 



81 






82 BUTTOLPH July 

distribute in occupied places without risk or inconvenience to the 
occupants. 

A variety of germicidal lamps is commercially available. All of 
them are basically low-temperature, low-pressure, electric-discharge 
lamps containing mercury vapor. They are electrically and physically 
identical with or similar to corresponding tubular fluorescent lamps 
except that they are made with special glass tubes transmitting the 
2537-angstrom energy with about the same efficiency with which, in 
fluorescent lamps, phosphor powders convert this same ultraviolet 
energy to longer wavelengths of visible light readily transmitted by 
ordinary glass tubing. The energy-conversion efficiency of these 
lamps is such that of the total electrical-energy input to the tube and 
ballasting device from 10 to 20 per cent is emitted as germicidal ultra- 
violet. For example, a typical commercially available 30-watt 
germicidal lamp and its ballast taking approximately 40 watts elec- 
trical input will produce 7 watts of germicidal ultraviolet. 

An even greater variety of germicidal fixtures than of lamps is 
commercially available. All of them provide for the proper electrical 
operation of the lamp and, except when intended for duct use, are 
equipped with enclosing reflectors, and sometimes louvers. Such 
fixtures should be carefully designed to keep the ultraviolet energy 
away from the occupants of a room and to prevent its ineffective dis- 
sipation through short distances to near-by walls and ceilings. In 
meeting such specifications these fixtures become ultraviolet-energy- 
projecting devices providing a fanlike distribution of ultraviolet 
energy in planes inclined 10 to 20 degrees above the level of the 
germicidal lamps, Fig. 1. Since such fixtures may vary greatly in 
their effectiveness, depending upon the reflector contours and ma- 
terial, they should be chosen with care to suit their operating locations. 
Of the total ultraviolet output of the bare germicidal lamps, such 
fixtures may emit 25 to 50 per cent giving them an over-all efficiency 
in terms of the electrical input of 5 to 10 per cent, over-all efficiencies 
still considerably higher than are secured with incandescent lamps in 
spotlighting equipment of comparable optical characteristics. 

Air disinfection in the auditoria, the accessory small rooms, and in 
the air ducts of theaters, can be done with germicidal lamps in accord 
with theoretical investigations 10 and engineering interpretations 11 
backed by considerable practical experience in medium-sized rooms. 
The theater auditoria provide, however, unique opportunities to take 
advantage of the fact that, because the air absorption of germicidal 



1948 ULTRAVIOLET AIR DISINFECTION 83 

ultraviolet is negligible, the effectiveness of germicidal lamps goes up 
linearly with the room dimensions. 

The installation of germicidal lamps in the motion picture theater 
presents two problems not encountered in hospitals, schoolrooms, 
offices, or even the theater presenting stage shows. These problems 
result from the fact that along with the ultraviolet from germicidal 
lamps there go, inseparably, 3 or 4 lumens of visible blue light per 
watt of tube input which, aided by the Purkinje effect in a darkened 
theater, becomes visible to an extent out of all proportion to the lamp- 
tube brightness or the illuminated walls and ceilings. 

The general auditorium- or balcony-installation practice is to place 
the germicidal fixtures as low as possible on the side walls in or 
slightly above a plane passing from the head level of standing patrons 
in the back of the auditorum or balcony to the top of the projection 
screen. With properly designed and sometimes louvered fixtures, such 
a placement will keep the germicidal lamps themselves out of sight of 
anyone in either the auditorium or balcony, although this results in 
rather high placement of fixtures over the front balcony in the older type 
of theaters with high balconies over a shallow auditorium. The usual 
low-ceiling-room practice can prevail in the portion of the auditorium 
under the balcony. 

The problem of blue light reflected down into the auditorium and 
down onto the projection screen from the ceiling and side wall is not so 
easily solved. In theaterswhere an unusually dark auditorium is main- 
tained during projection, light from the germicidal lamps scattered 
from the side walls and ceiling may be objectionable, especially during 
the proj ec tion of Technicolor pictures. This problem results primarily 
from the light reflectance of the ceiling and side walls but is also de- 
pendent upon the ultraviolet and light-distribution characteristics of 
the fixtures used. Although all ultraviolet and light from the fixture 
eventually must reach the ceiling and side \valls somewhere, the light 
is much less objectionable on the side walls than on the ceiling; for 
this reason, in theaters with light-colored walls or lower-than-usual 
ceilings, or with a high balcony necessitating placing the fixtures rela- 
tively near the ceiling, only louvered low-ceiling-type fixtures of the 
spatial distribution shown in Fig. 2 should be used. In theaters 
without a balcony, and especially those with side walls and ceilings of 
light reflectances less than 25 per cent, the basic open type of generally 
available fixture usually can be used. 

In this connection it should be noted that in those theaters providing 



84 BUTTOLPH July 

sufficient illumination of the projection-screen surroundings to re- 
duce contrast glare, in accord with recent good illumination practice, 
the problem of blue light scattered to the screen may not exist. Even 
with rather highly reflective ceilings and side walls, the total lumens | 
of light in the theater is only that usually provided by the stand-by 
illumination in theaters where patrons may find their seatswithout the 
assistance of aisle lights or flashlamps. When the installation of 
germicidal lamps is anticipated in a theater design or decoration, the 
apparent amount of blue light can be almost completely controlled by j 
the choice of wall and ceiling treatment, generally for reflectances of 
less than 25 per cent. 

Since the blue light from germicidal lamps is accompanied by about 
the same amount of energy in the near ultraviolet, of the wavelength 
frequently used in theaters for the fluorescent activation of carpets 
and decorative wall treatments, there are unexplored possibilities of 
using fluorescent wall treatments to replace relatively high reflectance 
of visible light with very low-level fluorescence by the near ultra- 
violet to produce just visible decorative patterns without objection- 
able reradiated or reflected energy to the projection screen. 

Fortunately, there can be considerable freedom of choice as to the 
location of germicidal fixtures on the theater side walls as nonuni- 
f ormity of ultraviolet distribution in space is amply offset by the ran- 
dom circulation of the air during the process of disinfection. Every 
effort should be made to fit the germicidal lamp into the architectural 
and decorative features of its surroundings even to the extent of en- 
closing stock fixtures in custom-made enclosures. It is often very 
difficult to adapt germicidal fixtures to the conventional architecture 
of older theaters but, fortunately, many fixture designs are adaptable 
to the modern treatments of theater interiors. 

Since the ozone-producing ultraviolet from germicidal lamps is 
completely absorbed by a few inches of air, the small amount of ozone 
they produce does not increase with the room dimensions as does the 
air-disinfecting action of the unabsorbed germicidal ultraviolet. For 
this reason ozone is not likely even to be detectable in a ventilated 
theater nor at all objectionable for such an installation as has been 
suggested for accessory rooms. 

Experience indicates that a normal germicidal-lamp installation is 
of value for odor control in the theater. The effect is easily observed 
but difficult to measure. The ultraviolet may promote the oxidation 
of odorous substances, usually of an unstable chemical nature 



1948 



ULTRAVIOLET AIR DISINFECTION 



85 



anyhow, either directly or by way of the very active form of oxygen 
present in the air from the formation and decomposition of ozone. 
The ozone itself also doubtless has a desensitizing action on the nose 
analogous to the effect of certain sound and light waves, or of certain 
flavors on the corresponding senses. It is interesting to note that this 
odor suppression seems to be effective under conditions where the 
ozone itself is barely if at all detectable. 

Manufacturers of fixtures suitable for theater use provide installa- 
tion tables based upon the room dimensions and ceiling heights, al- 
though few such tables are extended to the dimensions of theater 
auditoria. Table I is an attempt to consolidate in a single relatively 

TABLE I 

NUMBER OF 30- WATT LAMPS FOB 99 PER CENT UPPER- AIR DISINFECTION (BASED 
ON 6.5 ULTRAVIOLET WATTS OUTPUT AT 100 HOURS) 





Average Room 


















Dimensions 


12-23 


24-35 


36-47 


48-61 


62-73 


74-85 


86-97 




Over 25 




1 


2-3 


4-5 


6-7 


8-9 


10-11 





15 




1 


2-3 


4-5 


7-8 


9-11 


12-13 


o 

^ bC 

111 

33* 


10 

7 
5 
4 


1 
1 
1 
1-2 


1-2 
2-3 
2-4 
3-5 


3-4 
.4-5 
5-7 
7-10 


5-6 
7-8 
9-11 
13-16 


8-9 
10-12 
14-18 
20-25 


11-13 
15-18 
21-25 
29-34 


15-16 
21-24 
29-33 
39^4 





3 


2-3 


4-6 


9-14 


19-23 


28-34 


39^5 


51-57 



compact form a recommendation based on the most commonly used 
germicidal lamp, the so-called hot-cathode 30-watt type. By "Aver- 
age Dimension" is meant a figure obtained by dividing by two the sum 
of the length and breadth of the volume under consideration. The 
theater with a balcony should be broken up into three areas, the front 
auditorium, the auditorium under the balcony, and the area above the 
balcony. In such a large theater, the increased effectiveness of fix- 
tures in the larger-dimensioned front auditorium is fully offset by 
greatly decreased effectiveness under and over the balcony. It is also 
important to note that under and over the balcony only louvered fix- 
tures should be used and but one half as many as are specified by Table 
I to secure a theoretical upper-air disinfection of 90 instead of 99 per 
cent. Only an exceptionally dark treatment of the ceilings over these 
areas will permit the use of the full number of lamps specified by the 
table. 

The simplest case of the theater or auditorum is that without a 



86 BUTTOLPH July 

balcony, with dimensions of about 70 by 100 feet, and with a 30- to 
40-foot ceiling height. A seating capacity of 1000 may be considered 
representative of such a theater. The average dimension of 85 feet 
and the possibility of a 20- to 30-foot fixture-to-ceiling distance indi- 
cates, Table I, the need of a total of 8 to 10 units (depending upon the 
type) to provide a 99 per cent theoretical upper-air disinfection. This 
is provision for a lower-air disinfection at a rate equivalent to about 
100 air changes per hour. 

In the case of a theater with a balcony the calculation should be 
broken up into three parts, the open space above the front orchestra 
section, the orchestra area under the balcony, and the space over the 
balcony. A typical larger theater with balcony and seating about 
2000 people would have an orchestra area about 90 feet wide and 90 
feet deep, one half of it being under a balcony, 90 feet wide and about 
60 feet deep. The ceiling height over the front orchestra would be 
about 50 feet, over the back orchestra 12 to 18 feet, and over the 
sloping balcony 25 to 10 feet. 

Table I calls for 6 to 8 lamps for an average room dimension of 65 to 
70 feet and a fixture-to-ceiling distance of over 15 feet, but for theame 
area under the balcony, with an average fixture-to-ceiling distance of 
7 feet, one half the listing of Table I for accessory rooms or 5 to 7 
units should be used. Similarly, for the area above the balcony, with 
an average dimension of 75 feet and an average fixture-to-ceiling dis- 
tance of 10 feet, 6 to 8 units would be needed. The total lamp re- 
quirement for the seating area of the theater thus would be about 20, 
or one 30-watt lamp for 100 patrons. 

Small accessory lounging rooms and wash rooms with low ceilings 
may be handled in accord with the lower left of Table I. 

To make the recirculated air carried by the theater-ventilating and 
-heating duct system equivalent to outdoor air for sanitary ventila- 
tion, the same germicidal lamps used for upper-air installation may be 
installed directly in the ducts, but the number required is not so 
easily determined as for the upper air of the room because of the high 
and variable air speed and the great variations in duct shapes. 

For ducts whose greater dimension does not exceed the lesser by 
more than 50 per cent, and with nonreflecting walls, the maximum 
lamp requirements for a 99 per cent disinfection may be read from 
Table II. If the cubic feet per minute of air flow is not known it may 
be calculated as the product of the duct cross section, in square feet, 
and the air speed in feet per minute. 



1948 



ULTRAVIOLET AIR DISINFECTION 



87 



Note .in the following table that the cubic-feet-per-minute figures 
in the body of the table are directly proportional to both the number 
of lamps and the lesser dimension of the duct so that the tables may 
be expanded indefinitely by direct proportion and by lamp addition. 
For example, the requirement in 30-watt lamps for 220,000 cubic feet 
per minute of air carred by a 120- X 150-inch duct would be 10 times 

TABLE II 

GERMICIDAL-LAMP REQUIREMENTS FOR 99 PER CENT DISINFECTION OF DRY AIR 

IN NONREFLECTIVE CIRCULAR OR NEARLY SQUARE DUCTS, 

CUBIC FEET PER MINUTE 

Number of 30- Watt Germicidal Lamps 



Q 




1 


2 


3 


4 


5 


6 


7 


5 

6 


100 
120 


200 
240 


360 










cf 

o 


7 


140 


280 


420 


560 








II 

g 


8 
9 


160 

180 


320 
360 


480 
540 


640 
720 


800 
900 


1,080 




3^ 


10 


200 


400 


600 


800 


1,000 


1,200 


1,400 


;_i 


11 


220 


440 


660 


880 


1,100 


1,320 


1,540 


1 


12 


240 


480 


720 


960 


1,200 


1,440 


1,680 


I- 3 


13 


260 


520 


780 


1,040 


1,300 


1,560 


1,820 




14 


280 


560 


840 


1,120 


1,400 


1,680 


1,960 




15 


300 


600 


900 


1,200 


1,500 


1,800 


2,100 



Number of 30- Watt Germicidal Lamps 







7 


8 


9 


10 


20 


30 


40 




20 


2,800 


3,200 


3,600 


4,000 


. . 








25 


3,500 


4,000 


4,500 


5,000 








q 


30 


4,200 


4,800 


5,400 


6,000 


12,000 






o 


35 


4,900 


5,600 


6,300 


7,000 


14,000 






'% VI 


40 


5,600 


6,400 


7,200 


8,000 


16,000 






II 


45 


6,300 


7,200 


8,100 


9,000 


18,000 


27,000 




5 


50 


7,000 


8,000 


9,000 


10,000 


20,000 


30,000 




HI 


55 


7,700 


8,800 


9,900 


11,000 


22,000 


33,000 




1 


60 


8,400 


9,600 


10,800 


12,000 


24,000 


36,000 


48,000 


J3 


65 


9,100 


10,400 


11,700 


13,000 


26,000 


39,000 


52,000 




70 


9,800 


11,200 


12,600 


14,000 


28,000 


42,000 


56,000 




75 


10,500 


12,000 


13,500 


15,000 


30,000 


45,000 


60,000 




80 


11,200 


12,800 


14,440 


16,000 


32,000 


48,000 


64,000 



The above duct ratings are for a duct-air temperature of about 85 degrees Fahren- 
heit. These ratings should be decreased 10 per cent for temperatures of either 75 
or 100 degrees Fahrenheit, by 20 per cent for 65 or 115 degrees Fahrenheit, and by 
30 per cent for 60 or 125 degrees Fahrenheit. 



88 BUTTOLPH July 

the 9 lamps required for 10,800 cubic feet per minute in a 60-inch duct, 
or 90 lamps. 

For a 95 per cent disinfection but seven tenths the above number of 
lamps may be used, for 90 per cent one half, and for a 70 per cent dis- 
infection only one quarter as many. Installations to deal with bac- 
teria that have been exposed to a relative humidity greater than 60 
per cent and to deal with fungi require many more lamps than are 
called for in the preceding tables and should be treated as special cases 
for which engineering data are available elsewhere. 

In the frequent case of flat ducts having one dimension two or more 
times as great as the other there should be reference to more detailed 
methods of calculation available elsewhere but the maximum lamp 
requirements may still be determined from the preceding tables by 
subdividing the duct, and the air capa'city, so that the dimensions of 
the subdivisions fall within the range of the tables. For example, a 
2- X 9-foot duct carrying 9000 cubic feet per minute should be 
treated as 3 ducts each 2X3 feet and carrying 3000 cubic feet per 
minute. The tables call for a maximum of eighteen 30-watt lamps, 
but if the duct is calculated as a whole by a more adequate method the 
number is reduced to 15 lamps. 

The mechanical details of a germicidal-lamp installation follow 
closely those of the dust-filter installation and it is anticipated that 
manufacturers will provide similar standard-unit assemblies. Al- 
though there are many ways of installing germicidal lamps in air 
ducts, the best compromise on the mechanical and radiation factors 
calls for placing them lengthwise on the duct wall, on 4- to 5-inch 
centers grouped in the center half of the duct walls and out of the 
corners of rectangular ducts. The duct walls near the lamps and the 
duct width in both directions from them should be of polished chro- 
mium plate or aluminum if the conditions are such that the reflective 
duct walls can be easily cleaned whenever the lamps are cleaned. 
Standard wiring-channel strips, such as are used with the correspond- 
ing fluorescent lamps, may be attached to the outside walls of the duct 
with the lamp sockets projecting through holes in the duct walls and 
the reflector lining. Two-lamp assemblies using high-power-factor 
ballasts and moistureproof lampholders, especially designed for this 
type of installation are commercially available. 

Since the germicidal lamps must be kept reasonably free of dust, 
there must be convenient access for cleaning. This usually can be 
arranged by hinged panels on the sides or the bottom of the duct, and, 



ULTRAVIOLET AIR DISINFECTION 



89 



if necessary, the lamp may also be mounted on these panels as well as 
on the stationary duct walls, Figs. 3A and C. Where the mechanical 
conditions demand it, the lamps may, of course, be installed end to end 
along the duct. In any case, the reflector lining should be used on all 
walls of the duct and should extend beyond the ends of the lamps a 





(B) 





-12- 



(C) (D) 

Fig. 3 Schematic of germicidal lamps in ducts. 

distance twice that to the opposite side of the duct. If chromium- 
plated sheet steel is not available aluminum-foil-surfaced building 
paper or board, or certain special aluminum paints may be used as 
substitutes. 

In large ducts and plenum chambers germicidal lamps may be 
assembled like the rungs of a ladder in vertical frames supported out 



90 BUTTOLPH Jllly 

in the center of the chamber in whatever series or multiple arrange- 
ment best fits the local conditions and provides access for cleaning 
and replacement, Fig. 3D. In very large ducts, where the air speeds 
are relatively low, the lamps should be so placed, when possible, as to 
provide a maximum average distance from the lamps to the duct walls 
in directions perpendicular to the lamp tubes, and regardless of the 
direction of air movement. 

There is a special installation problem in case of flat ducts which 
may have one dimension 4 to 6 times the other. Such a duct cross 
section limits the effectiveness of the lamps not only in proportion to 
the lesser dimension but also because but little of the duct volume be- 
yond the actual location of the lamps is useful for air irradiation. In 
such cases the lamps should be distributed only over the longer duct 
walls to within the lesser dimension from the edges, Fig. 3B. 

In spite of the desirability, for efficiency, of the longest possible 
travel of the ultraviolet before the first reflection, it is sometimes de- 
sirable to combine the bactericidal treatment of air with the humidi- 
fying, filtering, and heating treatment it gets in an air-conditioning 
system. In such cases, it is desirable, when possible, to provide the 
bactericidal treatment at a point of average air temperatures, away 
from very hot air or very cold make-up air to maintain germicidal 
output efficiency. When possible, the lamps should be placed after 
the filtering which reduces the lamp cleaning, but before the humidi- 
fication which tends to increase the tolerance of bacteria for germicidal 
ultraviolet and may, in extreme conditions, cause electrical trouble* 
in lampholders and starters mounted in the chamber with the lamps. 

The fact that statistical evidence as to health value to the individual 
patrons from air disinfection cannot be secured, because of the small 
amount of their total time spent in the theater, is obviously no reason 
for not providing sanitary ventilation along with other recognized 
sanitary precautions to reduce the possibility of the spread of respira- 
tory disease in the theater. 

REFERENCES 

(1) M. Luckiesh, A. H. Taylor, and L. L. Holladay, "Sampling devices for air- 
borne bacteria," J. Bact., vol. 52, p. 55; July, 1946. 

(2) M. Luckiesh, A. H. Taylor, and T. Knowles, "Killing air-borne respiratory 
micro-organisms with germicidal energy," /. Frank. Inst., vol. 244, p. 267; Octo- 
ber, 1947. 

(3) W. W. Coblentz and H. R. Fulton, "A radiometric investigation of the 
germicidal action of ultra-violet radiation," Sci. Paper, no. 495, Bvr. of Stand., 
Jour. Res., vol. 19, p. 641; 1924. 



1948 ULTRAVIOLET AIR DISINFECTION 91 

'(4) Alexander Hollaender, "Abiotic and sublethal effects of ultraviolet radi- 
ation on microorganisms," Amer. Assoc. Adv. Sci., Symposium on Aerobiology, 
publication no. 17, p. 156; 1942. 

(5) L. R. Roller, "Bactericidal effects of ultraviolet radiation produced by low 
pressure mercury vapor lamps," J. Appl. Phys., vol. 10, p. 624; September, 1939. 

(6) H. C. Rentschler, Rudolph Nagy, and Galina Mouromsefif, "Bactericidal 
effect of ultraviolet radiation," /. Bad., vol. 41, p. 745; June, 1941. 

(7) W. F. Wells, "Bactericidal irradiation of air," /. Frank. InsL, vol. 229, p. 
347; March, 1940. 

(8) Ellice McDonald, "Progress of the bio-chemical research foundation," 
J. Frank. InsL, vol. 242, p. 435; January, 1947. 

(9) M. Luckiesh and A. H. Taylor, "Determining and reducing the concentra- 
tion of air-borne micro-organisms," Amer. Soc. Heat, and Vent. Eng., Journal 
Section, Heating, Piping and Air Conditioning, vol. 19, p. 113; January, 1947. 

(10) M. Luckiesh and L. L. Holladay, "Tests and data on disinfection of air 
with germicidal lamps," Gen. Elec. Rev., vol. 45, p. 223; April, 1924. 

(11) L. J. Buttolph, "Principles of ultraviolet disinfection of enclosed spaces," 
Amer. Soc. Heat, and Vent. Eng., Journal Section, Heating, Piping and Air Condi- 
tioning, vol. 17, p. 282; May, 1945. 



FORTY YEARS AGO 

Moving Picture Operators Dread the Summer 

Moving picture machine operators dread the approaching hot weather. 
Already they have experienced some of the discomforts that the Summer 
will bring. When the temperature commences to remind one of the good 
old Summer time and the mercury starts to climb, the stuffy little pic- 
ture booths become so hot and the air so stifling that it is almost impos- 
sible to remain in them any great length of time without going out to 
get a whiff of the fresh air. Even in the Winter time it is necessary to 
keep revolving fans constantly in motion to overcome the heat gener- 
ated by the powerful rheostats. In Summer the conditions are well-nigh 
unbearable. Up to this Summer the machine owners adopted their own 
methods of constructing their booths and ventilating them. Recent 
State restrictions have compelled them to enclose the machines in as- 
bestos fireproof booths of certain dimensions, and these are like sweat- 
boxes while the carbons are burning, the heat from them and the rheo- 
stats being intense. 

The Moving Picture World, May 16, 1908 



Theater Engineering Conference 

Ventilating and Air Conditioning 



Service and Maintenance of 
Air- Conditioning Systems* 

BY W. B. COTT 

WESTINGHOUSE ELECTRIC CORPORATION, NEW YORK 17, NEW 
YORK 

Summary Because of shortages of raw material and parts in the air- 
conditioning and refrigeration field, it is necessary that theater owners 
maintain and place in operation and service the apparatus already installed. 

THE OLDER TYPE refrigeration cycle installed prior to the develop- 
ment of the Freon refrigerants and the more modern refrigeration 
cycle is designed by the manufacturer and engineered by the installer 
to operate under exacting conditions and must be kept in clean, lubri- 
cated, and effective operating condition for satisfactory operation. 

The product of the manufacturer of air-conditioning apparatus, such 
as refrigeration compressors, condensers, water-saving devices, de- 
humidifiers, coils, heating elements, fans, motors, switches and start- 
ers, thermostats, and diffusers, is a result of painstaking research 
and diligent effort to produce a lower-cost product that can be mar- 
keted in a highly competitive business. 

These products are assembled by an installer or contractor together 
with ducts, wiring, insulation, and piping, for a purchaser into an in- 
stalled air-conditioning system. The reliable installer will design an 
air-conditioning system for low maintenance costs taking into con- 
sideration motor horsepower required, hours of operation, cost per 
kilowatt-hour, lubricants required, paint, accessibility of service 
valves and switches, worn parts replacement, and countless other 
factors. The final picture presented to the buyer by the reliable in- 
staller is the total cost in dollars out of pocket to the owner over a 
given period of time. Low first cost is not always the cheapest hi the 
over-all picture. 

Check the layout of your equipment room to see that a mainte- 
nance man will have sufficient room to check and lubricate apparatus. 

* Presented October 24, 1947, at the SMPE Convention in New York. 
92 JULY, 1948 JOURNAL OF THE SMPE VOLUME 51 



MAINTENANCE OF AIR-CONDITIONING SYSTEMS 93 



Lubrication points, valves, and gauge parts that are not accessible are 
seldom checked. The best of mechanical equipment breaks down 
occasionally or must be overhauled and ample room will result in a 
faster, better repair job with resultant low cost and the system placed 
in operation quicker. 

An air-conditioning system in a theater represents a sizable invest- 
ment to the purchaser and replacement of apparatuses high in equip- 
ment cost and delay involved in procuring parts together with quali- 
fied installation labor. The owner of an air-conditioning system 
must arrange service and maintenance of his plant to assist in prevent- 
ing breakdowns that result from lack of attention to the entire air- 
conditioning system including a check of the system for Freon leaks, 
particularly at the compressor seal, inspection and cleaning of drains, 
the inspection and adjustment of all belts, safety controls and temper- 
ature-regulation devices, and the cleaning and adjusting of all water 
valves, sprays, pumps, starters, and gauges, the lubrication of motors 
and bearings, the cleaning or 'replacement of air filters, and the adjust- 
ment of dampers. Prompt replacement of* worn parts is imperative 
in view of required operation of a plant and the annoyance attendant 
to a shutdown with loss of business. Periodic service and maintenance 
checks will enable you to keep a full charge of refrigerant in your plant 
and will locate leaks which may result in expensive repairs, loose fan 
belts or sheaves, and dirty filters that result in inefficient operation. 
Regular checks may reveal other defects prior to serious trouble. 

Various engineering societies and trade associations and all manu- 
facturers of this apparatus have drawn up service and maintenance- 
check charts with accompanying reports and varicolored or marked 
tags of plates to be attached to various check points to assist in check- 
ing and servicing apparatus. They have also prepared simple service 
and maintenance contracts for use in the trade. It is strongly urged 
that you contact the manufacturer, or his representative, of your 
refrigeration machinery and request his advice and recommendations 
regarding competent service and maintenance people and institute a 
periodic service and maintenance program. You will have many 
more hours of operation with less over-all expense in following the 
recommendations of the manufacturer and his accredited representa- 
tive who can supply factory parts and lubricants and who receive 
manufacturers' bulletins on products. 

Average costs of maintenance and service contracts, on a yearly 
basis, have been 19 to 27 cents per seat, dependent, of course, on the 
amount of equipment involved and the length of travel to the job. 



Theater Engineering Conference 

Ventilating and Air Conditioning 



Note: For the Theater Engineering Session on Ventilating and Air 
Conditioning, Chairman Seider requested that all discussion be held 
until after the Delivery of the last paper in the group. The material 
which follows, therefore, is in the nature of a panel discussion and 
deals with all four papers in this particular section. 

DISCUSSION 

MR. HUBERT: Mr. Kimball spoke about return diffusion wells in cooling sys- 
tems to get rid of. the water. At Lowell we found out that when we returned the 
water to the ground, depending, of course, upon the volume of water and the size 
of the return well, the well is effective for a period of about six months. Then it 
will take no more water. 

The pump man surges it with acid and it. commences to take water perfectly 
again. It lasts for three months this time. The next acid treatment lasts for 
about six weeks. About the fourth time, it is effective for about a day. 

Is there any way that you have had success in returning water 'to the well? 
The reason we aje interested in it is because the city has imposed a sewer charge 
on us; in other words, if you put water into your theater, then they charge you 
50 per cent of your water bill as a sewer charge. In the case where you are using 
well water, they meter the well and if you use 600 gallons a minute, they figure up 
what the cost would be. If you brought that water from the city, they charge 
you that much for a sewer charge. 

If we can return that water to the ground, we would save ourselves a great deal 
of money, but so far we have not been able to do it. Is there any way that you can 
assure a successful operation of these return wells over a period of time? 

MR. DWIGHT D. KIMBALL: You must be in a district where you have a peculiar 
subsoil condition. There is in New York State a limited area, largely around 
Long Island, where the State Conservation Commisssion requires return of water. 
I have had return diffusion wells that have been used for years without, such 
trouble. Once in a great while you get a condition where you have to surge a well, 
but it stands up for quite some time after that: 

I do not know what your problem could be, but you certainly must be in a strict 
area where you get these charges, because you can drill all the wells you want to, 
if you get permission of the State Conservation Commission and abide by their 
rules, but you do not pay any water rate. 

MR. HUBERT: As I understand it, the City spent about $150,000 in one year on 
municipal sewers. Under this new arrangement, they are going to collect about 
$2,500,000 a year on the water charge. 

However, our wells there are gravel wells. In most cases, the gravel is a mix- 
ture of anywhere from half an inch up to about two inches in diameter. The 
reason they started these return wells is that during the war the rubber companies, 
and similar plants, used an immense amount of water. They were using about 
75,000,000 gallons a day in the war industries. Naturally, the recovery is about 
94 






VENTILATING AND AIR CONDITIONING 95 




50,000,000 gallons a day. So they made them put the water in the ground, be- 
cause they could not keep the water table up; but they ran into trouble on the 

11s and the wells would not take it. 

We were formerly using 800 gallons a minute in our cooling system, when it was 

street-water job. We have now installed refrigeration, and we have four thea- 
there. Two hundred a minute is the smallest and about 450 is the largest. 

MB. W. B. COTT: We found in our experience, particularly in our own plant, 
that if you alternate the use of waste wells, you will prevent the silting up of the 
gravel there. Louisville has a very low water table. There is a range of hills 
back of Louisville that lowers the water table ; and as you get down to the flat of 
the river, alternate the use of the wells. As an example, we are drilling one well 
to put the water in now. Another well to put the water, in fifty to sixty days, 
helps considerably there. The wells have not been silting up so fast as they have 
been in the past. 

It might be well for you to examine the possibility, with your well contractor, of 
drilling additional wells for their disposal; that is, alternate the use of wells, one 
in this period of time and the other in the next period of time. 

MB. HUBEBT: We have never tried that. The Deal Pump and Supply Com- 
pany near Louisville used to drill quite a few of those wells, and now they have 
given up the idea of drilling return wells for the people, because everything has 
been tried to keep them from liming up, but they always do, except for a short- 
term operation where you want to use it for six months, then it is all right and they 
will drill a return well. However, if you have the idea of using it over a period of 
time, it is a waste of money. The liming process takes place over quite a large 
area, and forms a large cone there. When you surge it, you just push this liming 
process away from the well. Then it limes up to the well again. When you treat 
it again, it pushes it farther. Eventually, it gets so limed up that you cannot push 
it out, and that is why the well quits altogether. 

If you drill two or three wells and alternate them as you suggest, would not that 
be a case of prolonging the process until your wells lime up again? 

MB. COTT: I do not think so. The various whiskey distilleries there return 
their condenser water and the processed water to alternate wells. 

MB. PHELAN: Mr. Kimball, I was impressed by your costs on filters, but, in 
mentioning a throwaway-type filter costing $500, that is only the initial cost. 

MB. KIMBALL: Yes. 

MB. PHELAN: Do you not think that we should consider what they will cost 
over a period of time in comparison to the electric filter, where the operating cost 
only amounts to what an electric light bulb would use? 

MB. KIMBALL: The difficulty is that most theater people want to make their 
investment returnable in matters of replacing material on a basis of something like 
four to six years, and you do not come out even on that basis. If you can do it 
over a longer period of years, you have a saving in favor of the electrical. How- 
ever, they look too much not alone on this, but on their investment costs. 

MB. PHELAN: When you enter into the cleaning costs, the drapery costs, and so 
forth, I think that that would pull down the over-all cost on them, too. 

MB. KIMBALL: It is pretty hard to get a theater man to take that into account. 
I venture to say here in the Times Square district, you can go to theater after 
theater and most of them have not been redecorated since they were built. 



96 DISCUSSION July 

MR. ROBERT LEWIS: Dr. Buttolph, I have been using ultraviolet disinfecting 
lamps for some time. I have observed two factors. First, the reflectors on these 
lamps, apparently, by virtue of their being pointed upward, act as sort of a catch- 
all for dead bugs, silting, and other things. Second, apparently, there is a degen- 
eration of the glass envelope, either by bombardment at the end or by a general 
glass degeneration. 

I am well aware that you are required to have decent reflector performance, but 
the thing which struck us as peculiar was that it appeared to us after a period of 
not more than a day or so, that these small dusty positions on the reflectors ap- 
peared fluorescent. We wondered if you have any figures on that type of prob- 
lem and efficiency, and, second, what is the average life you should expect from 
glass envelopes. 

DR. L. J. BUTTOLPH: The germicidal lamps themselves depreciate very rapidly 
the first few hours and the first day of operation. As a matter of fact, they are 
officially rated after 100 hours of operation, to offset that to some extent. After 
that, they depreciate about the way fluorescent lamps do. 

The problem of collection of dirt on the reflectors is exactly the problem you 
have with lighting fixtures. If the installation has been engineered with an ade- 
quate factor of safety, that is not too serious a matter, however; but it is impor- 
tant that you originally specify two or three times as much germicidal ultraviolet 
as is really necessary, just to take care of those variations. 

MR. LEWIS: 'Perhaps I did not make the question quite so precise as I should. 
It was our observation that the effectiveness of the reflector was zero after a day. 

DR. BUTTOLPH: No, it is not that bad. We have measured many of them. 
The ordinary dust that settles on the reflector acts as a neutral filter between the 
particles. You can get dust absorption up to 25 or 50 per cent, but your instal- 
lation should take care of that. Again, it is the same problem that you have with 
an installation for illumination. 

MR. LEWIS: I believe that ultraviolet of that wavelength is not the same prob- 
lem as illumination. Otherwise, I think it is an answer. 

MR. ALBERT STETSON : Mr. Cott commented on the fact that the cost of service 
had been accelerated upward. He said that it was now running from 23 to 27 
cents. I believe he means 23 to 27 cents per seat per year. 

MR. COTT: That is correct. 

MR. M. D. KICZALES: Mr. Cott mentioned the use of ammonia refrigerant in 
air-conditioning systems. I am curious to know what states permit the use of 
ammonia in air-conditioning systems. 

MR. COTT: There are quite a few ammonia systems installed; in fact, I can 
take you within seven blocks of the hotel you are in, and show you four. 

MR. KIMBALL: In places of public assembly? 

MR. COTT: Yes, sir, in old equipment. They are carefully trapped and they 
are carefully watched by the City of New York. There' are several theater in- 
stallations using ammonia in Chicago and several in New Orleans. However, 
we have been trying to sell those people replacement equipment in the past. It 
may amaze you to know that there are six installations within the city limits of 
Manhattan, using methyl chloride, which is highly poisonous and highly dangerous. 
As a matter of fact, it is equipment that we as a manufacturer have a responsibility 
for now, because we purchased the company that made the methyl chloride. 



1948 VENTILATING AND AIR CONDITIONING 97 

MB. KICZALES: We agree that present codes in practically all states of the 
Union do not permit the use of ammonia. 

MR. COTT: That is true on new installations, but there are existing installations 
using those poisonous refrigerants. Under the new codes the use of ammonia 
refrigerants is not permitted. 

MR. KICZALES: Mr. Kimball, this afternoon we had quite a session on acoustics 
and the prevention of noise in the systems. Particularly, some recommendations 
were made to prevent the transmission of noise from air-conditioning equipment. 
One of the speakers recommended certain limitations in the design of air-con- 
ditioning systems primarily, saying that the air-supply ducts should be set at 500 
feet per minute, and the recirculating grill should be set at 250 feet per minute, in 
order to be safe and remain within the 35-decibel allowance for the theater. 

MR. KIMBALL: Those are, economically or from an engineering standpoint, 
rather absurd limits, because I do not know of any jobs installed with those very 
low velocities. If you take a large 1000-seat theater, particularly under the 
present rate, we could not get space in the building in many cases. However, I 
have used 1200, in some cases 1400 feet, for years without trouble; that is, in the 
main larger ducts. You get smaller ducts, of course, but we have no trouble if 
the duct work is substantially designed and built. 

MR. KICZALES : I made a recommendation like that this afternoon, and it seemed 
that certain architects and engineers did not hold to that stand, when I mentioned 
that we were using 1200- to 1400-foot velocity starting at the fan, and reducing as we 
go along down to the outlet. It went as far as 600 feet per minute at the outlet 
itself, and we wanted to design 400 to 450 at the recirculating grills. 

Mr. Kimball mentioned extending the air-supply duct into the lobbies in order 
to prevent a back draft from the opening of doors into the theater. I have very 
successfully made use of a concealed unit heater with a recirculating grill at the 
bottom, and filtering the air across the lobby entrance with proper controls at the 
ceiling and at the floor to give a proper temperature. That would heat the air be- 
fore it moved down the lobby into the rear of the theater. 

MR. KIMBALL: That is perfectly possible, but it lacks one advantage. If you 
install it as I suggest, you not only get heat in the winter, but you get air con- 
ditioning into the lobby in the summer. 

MR. KICZALES: With the air-conditioning system in the summer time, you can 
do with a lower air temperature in the lobby as it usually, passsing through, is 
more or less a cooling-off chamber to prepare you for the lower temperature in the 
theater proper. We use more or less the exhaust system from the lobby and pass 
it on through ; I mean, from the auditorium to the theater and then on out. That 
is the air you have to throw away normally. 

MR. KIMBALL: In the case of ultraviolet treatment, where in the theater would 
you place your lamp to meet the approval of the architect? Second, what would 
be the approximate cost of such a treatment, say, in a 1000-seat theater? 

DR. BUTTOLPH: In the old theaters, it is almost impossible to find any place 
that would satisfy even the architect who designed it, to say nothing of the modern 
ones. Fortunately, the modern theater designs are rather adaptable. We have 
one or two installations where they are perfectly adaptable.. They are horizontal 
wall treatments into which fixtures can be recessed, to be practically unnoticeable. 

The installation cost runs about $1.00 per seat. The lamp replacement cost is 



98 DISCUSSION July 

about 10 cents per seat. That cost does not include the maintenance, which can 
be thrown in with the maintenance of the illumination of the place, because there 
is just the matter of dusting up whenever they clean up the theater. 

MR. KIMBALL: I have had two occasions within the last two years of giving th<i 
theater a designed air-conditioning system, and the architect gave me the pro- 
nouncement that there should be no opening outlets in the ceiling or walls. If he 
will not permit air outlets, how will he allow those light outlets? 

DR. BUTTOLPH: That light outlet is a horizontal slot only about 6 or 7 inches 
high, at the most, and 3 feet long per unit. So it is not too conspicuous. It 
should be broken up by horizontal black louvers, and thereby mask the reflectors. 
So, it can be designed into a new place rather easily. 

MR. KIMBALL: The great problem in a theater is this: In a filled auditorium, 
you do not like sitting next to somebody who is coughing violently and sneezing. 
Will that ultraviolet treatment take care of such a condition? 

DR. BUTTOLPH: No, particularly not the psychology of that particular situ- 
ation. Glycol will handle that particular job, at least the psychology of it. I 
do not know whether it works fast enough to catch the drop in its foot of travel. 

MR. J. W. SPISELMAN : Dr. Robertson and his associates have recently pub- 
lished a paper in which they actually, by advanced methods of collecting air samples, 
have tested the exact killing rate. What they found was that the kill was so rapid 
within the first second that they could take their first air sample and see that at 
4east 80 to 85 per cent of the kill had been completed. That is within the first 
second of the injection of droplets simulating that of a sneeze or a cough. Within 
the second second, another 50 per cent of the remaining 15 per cent will be killed. 
At the end of the third second, they were down to virtually a zero count as far as 
the bacteria injected into the chamber was concerned. 

Other evidence, such as the direct spray into hospital wards, which I had men- 
tioned before, and into cages with mice and into other guinea-pig tests, has indi- 
cated that the glycol reaction is an extremely rapid one. 

I might point out that glycol has been used for years as a dehumidifying agent 
in massive absorbers; in other words, in much the same way that lithium chloride 
is used, the same way that silica jel is used. Triethylene glycol has been used 
as a chemical humectant, in a dehumidifying agent. 

In some installations, air flowing at the rate of 500 feet per minute over a distance 
of only some 2 feet, we can almost calculate how rapidly it is dehumidified. Air has 
been dehumidified from, let us say, 60 to 70 per cent humidity down to 25, indicat- 
ing a very rapid absorption of water. 

Conversely, the argument is that at that same rate of speed a moist particle will 
pick up glycol, indicating that the actual pickup of glycol must be an extremely 
rapid affair; and once the concentration has been formed on the bacterial particle 1 , 
death will take place. 

MR. KIMBALL: How quickly? 

MR. SPISELMAN : As quickly as medical men have been able to pick up an air 
sample. In this one particular piece of work, they feel that they picked it up with- 
in one half of one second, which is the first one that they want. At that time there 
was between 75 and 80 per cent of kill; in other words, they had that much less 
than they had sprayed in. I have heard that when ultraviolet kills germs, it will 
kill them just as quickly. 



1948 VENTILATING AND AIR CONDITIONING 99 

DR. BUTTOLPH: We think that the sneeze has been entirely overrated as a 
spreader of disease. The probability that an adjacent person actually will be 
able to inhale any considerable number of organisms from a particular sneeze is 
surprisingly remote. The rate of diffusion even in a foot or two, is rapid. In 
general, the inhalation is not so timed with the sneeze as to gather much of the 
contamination. It is largely a psychological problem. 

MR. KIMBALL: I was going to say you have a psychological problem, and you 
have confirmed it. 

MB. KICZALES: The American Society of Heating and Ventilating Engineers has 
always felt that the determination as to what germs are really effective and detri- 
mental in air-conditioning systems, was up to the medical profession itself and not 
up to mechanical engineers, I believe at the last meeting held about a year ago at 
Cleveland, there were some talks presented about the use of germ-killing means in 
air-conditioning systems, and no definite conclusion was reached as to whether 
they were needed or not, even in large air-conditioning systems. 

However, in my opinion, since we are talking about theaters in this particular 
meeting, where you are being exposed to germs for about two hours, I doubt 
whether there is any need for any germ-killing means in an air-conditioning system 
in a theater. From my small knowledge of the medical profession and germs, we 
find that there are germs in the air, but they are not all disease germs; that they 
will not attack the body. You can put a glass of water or a little globule of water 
under a microscope and you will find it crawling with germs, but it is still con- 
sidered pure water. They do not kill. They do not cause disease. I wonder how 
many germs there are in an air-conditioning system that do spread disease; 
whether it is economically sound to put in some kind of germ-killing apparatus. 
. DR. BUTTOLPH: The Society of Heating and Ventilating Engineers, through one 
of its committees on air disinfection and the Research Laboratory in Cleveland, 
is working on some research projects for the Society itself. It recognizes bacteria 
as one of the real contaminants of air, along with body odor and dust. There is 
IK (question about the recognition. Both the Society of Bacteriologists and the 
American Medical Association recognize that there is a problem. The Council 
of the American Medical Association has a setup by which it examines equipment 
for air disinfection. That does not happen to be on air ducts, but it does read on 
the need for air disinfection. 

MR. SPISELMAN: It has been part of the work that I have done, although I am 
an engineer. I have set out dishes and I have collected some of these plates that 
show the-amount of bacteria and germs that are in the air. I was interested in it, 
very much the same along the lines that your were, and I had a few medical men, 
bacteriologists, examine the plates. I was really amazed at the number of patho- 
gens that will fly around in the air. 

I have asked the same question: Just why doesn't it affect all of us? Quite 
often, the answer is that there is a certain threshold level to which you can with- 
stand the bacteria and the pathogens. Beyond that threshold level, which is de- 
termined by the concentration of those bacteria in the air, they start working on 
the various people, on some more than on others. 

Moreover, in a recent issue of Science Newsletter, I read that the cold virus is par- 
ticularly bad in that one respect : By the time you know you have gotten the cold, 
it has been in your body for a long time and has incubated. As a matter of fact, 



100 DISCUSSION 

they are trying to determine the rate at which a person does pick up a cold, if he is 
susceptible to it, and they have it down to within minutes once they have been ex- 
posed to it. That is about all I can say in reference to your question. 

MR. KICZALES : Has the medical profession ever stated that the air-conditioning 
systems in theaters do cause disease? Have they come out point-blank and stated 
that they should be provided with some germ-killing apparatus? No one has yet 
determined that some disease is caught in a theater. 

We cannot be too sure whether anyone caught the cold after he left the theater, 
whether the contact was made in a streetcar coming home, or on the street, or in 
the theater. I believe the purpose of the research being done by the American 
Society of Heating Engineers is to determine that. True, it is a project, but no 
definite determinations have been made by the committee as to what was needed. 

MR. SPISELMAN : I do not know whether any public health outfit has come out 
and said flatly that the theaters are a hotbed of disease or anything of that nature, 
but time and again I have picked up papers during epidemic periods, and one of 
the first places that you are warned to stay away from are theaters and places 
of public congregation. That of itself, coming out from individual public-health 
servants, quite probably shows what they must have in the back of their minds 
as to where the probable focal points of any disease or any epidemic may start. 
The same thing is applied to swimming pools and to other places of public 
congregation. By and large, they do not leave out the moving picture houses 
or the theaters. They usually see to it that those are included in the statements. 

MR. KICZALES: Someone should combat these statements by the public 
officials; that a theater owner should put in some sort of system just to advertise 
that he has some sterilizing equipment in his air-conditioning system. 

MR. NEIL WHITE: Mr. Kimball, in the average air-conditioning installation in 
a theater, what is the period over which a complete air recirculation takes place? 

MR. KIMBALL: It will vary to a certain extent with the density of the seating 
and the height of the theater; in other words, the cubic feet of space per person. 
However, they run around seven changes an hour on an average. 

MR. WHITE: I have had a little experience with one unit of this ultraviolet 
lamp. I seemed to detect a change in odor in the room, and as though there had 
been ozone generated or some ionization had taken place. 

DR. BUTTOLPH: All germicidal lamps, at least if they are built so that they are 
effective at all, produce minute amounts of ozone. It is a manufacturer's problem 
to prevent their producing too much. There is probably some odor masking due 
to the ozone. Other than that, germicidal ultraviolet is a remarkable photo- 
catalyst; that is, ordinary oxidation by oxygen goes on much more rapidly in the 
presence of germicidal ultraviolet. Probably both those things are effective. 
Practically, I believe there is no effective installation of germicidal lamps where 
there is not a noticeable change in odor. 

Recently, a number of companies started promoting the lamps purely for that 
purpose. They are entirely comparable with these recently advertised chemical 
substances for that purpose. We have chosen not to feature that, because we 
think that is a minor job the lamps can do in the long run. It is incidental to 
their more important use for air disinfection. 



Theater Engineering Conference 

Promotional Display 

Display Frames in the 
Motion Picture Theater* 



BY LESTER RING 

STANLEY DISPLAYS, INC., NEW YORK 18, NEW YORK 






Summary There is no need to enter upon the importance of displaying 
advertising in a theater. The reasons are too well known by all; but, the 
number of frames, type and size, are worth considering in planning the in- 
stallation of display frames. 



WHILE THERE EXISTS no history of the events leading to the 
evolution of the display frame, it may have begun with a fan- 
fare of trumpets, followed by a courier announcing a message, meant 
to reach as many as possible ; and when in later years we learned to 
read, the rescript was fastened to the side of a prominent building, 
thus starting the oldest form of what we know today as "billposting." 
There is still with us, on highways, barns, roof tops, and sides of 
buildings, in the form of 24 sheets and smaller sizes of lithographs, 
hand lettering, electric signs, and other forms of displays. 

The earliest print, I have seen, of a theater with posters on each 
side of the entrance, was the Globe Theater in London, where plays 
were written and produced by Shakespeare. 

Our own " Opera House" of yesterday used the three-sheet litho- 
graphed posters, 40 X 80 inches in size, pasting them to "House 
Boards" in front and around the theater. Such boards consisted of a 
wood backing with trim molding around the perimeter. Posters were 
pasted on over another, as each attraction played the theater. 

This method was used by the first theaters showing motion pic- 
tures; and, as producers and film exchanges started renting one- 
sheet and three-sheet lithographs, 11- X 14-inch photographs, and 
similar material, with a rebate upon their return in good condition, a 
need was apparent for their display without pasting. Thereupon, this 

* Presented October 24, 1947, at the SMPE Convention in New York. 

JULY, 1948 JOURNAL OF THE SMPE VOLUME 51 101 



102 RING July 

was done by thumbtacking, and in order to protect them from 
embryo artists and weather, a glass door was hung in place, the fore- 
runner of today's display frames. 

The number of frames is dependent on space available, as well as 
the policy of the theater, whether playing single or double features, 
and the number of changes per week. Frames, each side of entrance 
to theater, are always for "NOW SHOWING." Additional frames, on 
the front or side of the theater, may be used for "NOW PLAYING" or 
"NEXT ATTRACTIONS," those in the vestibule are usually for "NEXT 
ATTRACTIONS," and those in lobby and foyer for "COMING." It is im- 
portant that all frames be equipped to take the same layout of ad- 
vertising material, so that the advertising may progress from COMING 
to NEXT ATTRACTION, to NOW SHOWING, without additional purchases, 
or having some of it left over in the manager's office. The total num- 
ber of frames required for any theater cannot be worked out by 
formula, but from the foregoing, six frames, or two for each category, 
such as COMING, is the minimum. 

Types of frames are usually of wood or metal; wood frames should be 
of hard wood, such as walnut, oak, or birch. Metal frames should be' 
of such material as will obviate polishing, and aluminum should be 
anodized to prevent oxidation and pitting. 

With the indirect illumination of lobby and foyers with cove light- 
ing and pinpoint downlights, it has become necessary that display 
frames be illuminated from within. Contemplated theaters should 
make necessary provisions for this by providing recesses, and carrying 
electrical outlets' to them. In an existing theater, if cutting recesses in 
the walls, or furring the walls to create room for shadow boxes is in- 
advisable, display frames can be built out with suitable depth, creating 
shadow boxes within the display frame itself. 

The front or outside frames should be illuminated, even though the 
marquee may furnish sufficient light for readability of advertising 
matter; this is done to create a point of interest at all times, and 
especially when the marquee ceiling is not lit, as, between the time 
the box office closes and the break of the show. If fluorescent tubes 
are used for outside, they should be the low-temperature ones, to in- 
sure proper starting in cold weather. 

Fluorescent lighting and cold cathode are the two best media, em- 
bodying maximum illumination with less current consumption and a 
minimum amount of heat. Where sufficient recess depth of shadow 
box is available, approximately 12 inches, incandescent lights of 150 



1948 DISPLAY- FRAMES 103 

watts set in reflectors top and bottom 9 inches on centers, are very 
effective. Fluorescent and cold cathode should be installed on all four 
sides, for an even distribution of light. 

The size of frames is dependent upon policy and the number of 
changes for each theater. It is important, however, to use frames as 
large as possible, consistent with architecture and ceiling height. 
Frames should be a minimum of 40 X 60 inches and a maximum of 40 
X 80 inches inside for the individual frame with hinging sash. One 
opening sliding-glass frame can be 10 to 16 feet long and 72 inches high, 
glass size. The latter type should have but one sliding glass to each 
track, to prevent chipping and breakage. 

Since advertising material today is well standardized, equipment 
inside the frame to receive such advertising is easily arranged. Where 
double features are played, it is desirable to equip a frame to take ad- 
vertising of both pictures. Prominence can be given to one picture 
with stills or 11 X 14's of the cofeature. An ideal layout is a 30- X 
40-inch, date strip, cofeature title card, and two stills. 

Poster exchanges and frame manufacturers will be pleased to work 
out sizes of frames required for various layouts. Auxiliary stand 
frames can be used in a prominent location, to advertise a coming 
attraction, a list of future coming titles, or institutional copy. In some 
localities, building and public-assembly bureaus frown on stand 
frames, classifying them as hazards. 

Another* type of display is the banner, or reader board; this is a 
frame set above the entrance doors, and is used for COMING, NEXT 
ATTRACTION; and when placed above the first set of doors on the 
street side, NOW PLAYING. Lobby banner frames may have a trough 
of fluorescent or cold-cathode strips, top and bottom, or both, for 
greater visibility. To realize the maximum from this type of frame, 
it is advisable to have more than one banner board to progress the 
material. 



Society Announcements 



Convention Papers 

Preparations are being made for the Fall Meeting of the Society which will be 
held at the Statler Hotel in Washington, D. C., October 25 to 29, 1948, inclusive. 
Authors desiring to submit papers for presentation at this meeting are requested 
to obtain Author's Forms from the Vice-Chairman of the Papers Committee 
nearest them. The following are the names and addresses : 
Joseph E. Aiken N. L. Simmons 

225 Orange St., S. E. 6706 Santa Monica Blvd. 

Washington 20, D. C. Hollywood 38, Calif. 

E. S. Seeley R. T. Van Niman 

250 West 57th St. 4431 West Lake St. 

New York 19, N. Y. Chicago 24, Illinois 

H. L. Walker 
P. O. Drawer 279 
Montreal 3, Que., Canada 



Technical Societies Council Elects Officers 

On May 20, 1948, the Technical Societies Council of New York held its annual 
meeting and election of officers. Those elected were the following: 

PRESIDENT SECRETARY 

C. S.-Purnell W. F. O' Conner 

American Institute of American Chemical Society 

Electrical Engineers 

VICE-PRESIDENT TREASURER 

O. B. J. Fraser M. C. Giannini 

American Institute of American Society of Heating 

Mining and Metallurgy and Ventilating Engineers 

In addition, five of the six directors on the governing board were elected. 

The Council was incorporated one year ago with local groups of -fourteen lead- 
ing engineering societies, representing some 25,000 engineers in the metropolitan 
area, as charter members. Each society has two delegates to the Council, which 
serves as a medium for mutual professional betterment, more effective public 
service, the furtherance of high professional standards and the advancement of 
engineering and scientific knowledge. 



Journal Exchange 

To complete a set, copies are urgently needed of SMPE Transactions numbers 
1, 2 (1916); 5 (1917); 6, 7 (1918); 8, 9 (1919); 16 (1923); 18(1924); and 
30, 31 (1927). Will anyone who wishes to sell any of these numbers please 
write to R. Kingslake, Eastman Kodak Company, Rochester, New York. 
104 



Book Review 



Developing Technique of the Negative, by C. I. Jacobson 

Published (1948) by the Focal Press, Inc., 381 Fourth Ave., New York 16, 
N. Y. 309 pages + xiv pages + 10-page index. 52 illustrations. 5 1 /* X 7 l / z 
inches. Price, $3.50. 

This book describes in detail the process of converting an exposed photographic 
film into a negative. It makes no attempt to explain the why or wherefore of the 
processes involved. A knowledge of a certain minimum amount of physics and 
chemistry would be required were this included. Instead, word descriptions and 
"practical illustrations" are used throughout, to make the subject matter under- 
standable to the reader. As a result, one obtains a rather oversimplified picture 
of the developer technique, but the picture serves very well to an operator whose 
knowledge of science is limited. The more mature reader with a knowledge of 
chemistry, can also read the book with profit, for he would obtain a bird's-eye 
view of the entire field, one that can serve as an introduction for a later and more 
detailed study. 

The book describes the composition of the developer solution, the methods of 
formulating it, and the properties of the ingredients involved. It contains a 
somewhat extended discussion of the differences between the many concoctions 
that are now in common use as developers, grouping them into three general 
classes. This is a useful generalization as it enables the technician to choose a 
specific solution for a specific purpose. 

While the discussion of the developing solutions forms the -most important 
part of the book, it also contains sections on the aftertreatment of the negative. 
Not the least interesting of the extraneous matter is a chapter dealing with dark- 
rooms and darkroom equipment. Apartment-house dwellers will be especially 
interested in the section which describes how a lavatory can be converted into a 
darkroom. 

Several errors were noted, but these appear to be not too important. The most 
glaring of these appears on page 207. There it is noted that Kodak's D-76 and 
Ansco's A-17 are compounded with sodium carbonate as the energizer. These 
developers use borax. However, on page 153 the correct formula is given for 
D-76. 

The binding and the paper appear to be of good quality, a noteworthy event 
these days of inferior quality. The book will stand considerable thumbing, and 
it is the type of book that asks for such treatment. 

JOSEPH S. FRIEDMAN 

Ansco 

Johnson City, N. Y 



105 



Current Literature 



In the March, 1948, issue of Steelways, there appeared, on page 9, a popular 
article entitled "Report from Hollywood," by Hannibal Coons. Nails, steel tub- 
ing, structural steel, and other items made of this metal, are considered in rela- 
tion to their-use in the construction of motion picture studios and within the com- 
pleted buildings. 

Copies of Steelways may be obtained on request from 

The American Iron arid Steel Institute 

350 Fifth Avenue 

New York 1, New York . 



RCA Index 1947 

Recently the RCA Review issued a 24-page Index of substantially all published 
English-language technical papers on subjects in the radio, electronics, and re- 
lated fields, the author or a coauthor of which was associated with the Radio 
Corporation of America at the time of the paper's preparation or at the time the 
work described in the paper was performed. The full title of this booklet is 
"RCA Technical Papers (1947) Index Volume II (b)" and it may be obtained 
on request from the RCA Review, RCA Laboratories Division, Princeton, N..I. 



EMPLOYMENT SERVICE 



POSITIONS WANTED 

CAMERAMAN: Twelve years' experience in industrial pro- 
duction, three years as chief cameraman with commercial studio. 
Familiar with all types of work, 16 and 35, studio and location, 
black-and-white and color, sound and silent. Knows editing, 
sound and laboratory problems. Single, willing to relocate. 
Write P. O. Box 1158, Grand Central Station, New York 17, N. Y. 

CINEMATOGRAPHER: A-l references, wants employment with 
industrial company anywhere in the United States. Will travel 
any needed time. Experienced documentary, 35-mm and 16-mm, 
color or black-and-white. Active Member SMPE. Charles N. 
Arnold, P. O. Box 995, Peoria, 111. 

ENGINEER: Recent graduate B.S. in Mechanical Engineering 
from The University of Texas. Desires junior engineering posi- 
tion with a manufacturing firm in the motion picture industry. 
Background in mechanical and electronic equipment design. 
Write to A. Kent Boyd, 3308 Liberty, Austin, Texas. 



106 



Journal of the 

Society of Motion Picture Engineers 

VOLUME 51 AUGUST 1948 NUMBER 2 

PAGE 

Television Transcription by Motion Picture Film 

THOMAS T. GOLDSMITH, JR. AND HARRY MILHOLLAND 107 

Television Recording Camera 

J. L. BOON, W. FELDMAN, AND J. STOIBER 117 

Development of Theater Television in England . . A. G. D. WEST 127 

Auditorium Acoustics J. P. MAXFIELD 169 

Quieting and Noise Isolation EDWARD J. CONTENT 184 

Behavior of Acoustic Materials RICHARD K. COOK 192 

Continuously Variable Band-Elimination Filter 

KURT SINGER 203 

Society Announcements 211 

64th Semiannual Convention 212 

Book Reviews: 

"Magic Shadows," by Martin Quigley, Jr. 

Reviewed by John E. Abbott 214 

"Photographic Facts and Formulas," by E. J. Wall and 
Franklin I. Jordan 

Reviewed by Howard A. Miller 214 

Section Meeting 216 

Current Literature. ... 217 

New Products.. 218 



ABTHUR C. DOWNES HELEN M. STOTE GORDON A. CHAMBERS 

. Chairman Editor Chairman 

Board of Editors Papers Committee 



Subscription to nonmembers, $10.00 per annum; to members, $6.25 per annum, included in 
their annual membership dues; single copies, $1.25. Order from the Society's general office. 
A discount of ten per cent is allowed to accredited agencies on orders for subscriptions and 
single copies. Published monthly at Easton, Pa., by the Society of Motion Picture Engineers, 
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342 Madison Ave., New York 17, N. Y. Entered as second-class matter January 15, 1930, 
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Copyright, 1948, by the Society of Motion Picture Engineers, Inc. Permission to republish 
material from the JOURNAL must be obtained in writing from the General Office of the Society. 
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Society of 

Motion Picture Engineers 

342 MADISON AVENUE NEW YORK 17, N. Y. TEL. Mu 2-2185 
BOYCE NEMEC . . . EXECUTIVE SECRETARY 

OFFICERS 

1947-1948 

PRESIDENT EDITORIAL VICE-PRESIDENT 
Loren L. Ryder Clyde R. Keith 

5451 Marathon St. 233 Broadway 

Hollywood 38, Calif. New York 7, N. Y. 

PAST-PRESIDENT CONVENTION VICE-PRESIDENT 
Donald E. Hyndman William C. Kunzmann 

342 Madison Ave. Box 6087 

New York 17, N. Y. Cleveland, Ohio 

EXECUTIVE VICE-PRESIDENT SECRETARY 
Earl I. Sponable G. T. Lorance 

460 West 54 St. 63 Bedford Rd. 

New York 19, N. Y. Pleajsantville, N. Y. 

1948-1949 

ENGINEERING VICE-PRESIDENT FINANCIAL VICE-PRESIDENT 

John A. Maurer James Frank, Jr. 

37-0131 St. 18 Cameron PI. 

Long Island City 1, N. Y. New Rochelle, N. Y. 

TREASURER 

Ralph B. Austrian 
247 Park Ave. 
New York 17, N. Y. 

Governors 

1947-1948 

John W. Boyle Robert M. Corbin . Charles R. Daily 

1207 N. Mansfield Ave. 343 State St. 5451 Marathon St. 

Hollywood 38, Calif. Rochester 4, N. Y. Hollywood 38, Calif. 

David B. Joy Hollis W. Moyse 

30 E. 42 St. 6656 Santa Monica Blvd. 

New York 17, N. Y. Hollywood, Calif. 

1948 

William H. Rivers S. P. Solow R. T. Van Niman 

342 Madison Ave. 959 Seward St. 4431 W. Lake St. 

New York 17, N. Y. Hollywood, Calif. Chicago, 111. 

1948-1949 

Alan W. Cook Gordon E. Sawyer 

4 Druid PI. Lloyd T. Goldsmith 857 N. Martel St. 

Binghampton, N. Y. Burbank, Calif. Hollywood, Calif. 

Paul J. Larsen 

Los Alamos Laboratory 
University of California 
Albuquerque, N. M. 

Section Officers and Office Staff listed on page 220. 



Television Transcription by 
Motion Picture Film* 

BY THOMAS T. GOLDSMITH, JR. AND HARRY MILHOLLAND 
ALLEN B. Du MONT LABORATORIES, INC., PASSAIC, NEW JERSEY 

Summary The paper describes the electronic and camera equipment 
for recording television sight and sound on film, the picture made directly 
from the face of the cathode-ray tube. The application of this technique 
will be discussed with regard to documentary recording, network syndication 
use, and theater television. Representative films recorded in this manner 
are available. 

FOR OVER TEN YEARS Du Mont Laboratories have photographed 
television programs from the face of the cathode-ray tube using 
both still cameras and motion picture cameras. The early motion 
picture recording employed conventional cameras which were non- 
synchronous with the television system, and stroboscopic patterns 
of blanking, overexposure, and underexposure were present on the 
films. Later there was developed a synchronously driven camera 
operating at 15 frames per second, thus exposing one entire frame of 
television and skipping the next during pulldown. This camera, 
however, produced a nonstandard film making it difficult to utilize 
the picture either for regular viewing or for television rebroadcast. 

Since the camera equipment is specialized, we then approached 
Eastman Kodak Company to develop a commercial camera of this 
style. Boon, Feldman, and Stoiber describe this special camera 
developed for use in television transcription.** We shall discuss some 
of the electronic problems which arise in television transcription, and 
consider the use of transcriptions by the broadcaster, advertiser, and 
theater. 

Television transcription is accomplished by recording a program 
on motion picture film directly from the face of a cathode-ray tube. 
The sound-channel recording is done by conventional means but the 
picture recording is rather complex in order to achieve high quality. 
A major consideration is the fact that the television picture rate of 
transmission is 30 complete frames per second. On the other hand, 
the standard of motion picture recording is 24 frames per second. 

* Presented October 23, 1947, at the SMPE Convention in New York. 
** JOUKNAL OF THE SMPE, this issue, pp. 117-126. 

AUGUST, 1948 JOURNAL OF THE SMPE VOLUME 51 107 



108 



GOLDSMITH AND MILHOLLAND 



August 



We record the television pictures on film at the rate of 24 frames per 
second so as to allow reprojection of the film either in a conventional 
projector for direct viewing or in the standard projector for rebroad- 
cast by television. 

A transcription recording console consists of a special monitor 
receiver and a film camera, with associated sound-recording facilities. 
The photograph of Fig. 1 shows a special monitor of this type and the 
recording camera as constructed by Eastman Kodak Company. 
Particular precautions must be taken in the design of the monitor 
to eliminate as far as possible many of the fluctuations which are 
readily tolerated in home television receivers. For example, a high- 




Fig. 1 

voltage supply of excellent regulation is required so as to avoid any 
change in picture size with the variation of picture brightness in the 
scene being televised. The screen material of the cathode-ray tube 
must be very fine so as to be below the spot-size limit of the electron 
beam. Obviously, the linearity of scanning is adjusted as well as 
possible. A form of gamma correction is inserted so that to some 
degree the chemical gamma factor of the film can be matched to 
produce most faithful contrast gradations in the pictures. It is 
customary to use a positive picture on the monitor, but in some cases 
where speed is essential, a negative picture is produced on the monitor 
by means of video reversal of the signals which drive the cathode-ray 



1948 TELEVISION TRANSCRIPTION BY FILM 109 

tube. Where the negative picture is used, it is necessary to generate 
a reverse blanking signal in the equipment so as to suppress completely 
the normal synchronizing pulses, and obscure the return trace lines 
from the picture. If a system were being developed exclusively for 
theater television, the synchronizing signals could be in the whiter- 
than-white direction, and it would be unnecessary to have this com- 
plication. Where the negative polarity picture is reproduced on the 
cathode-ray tube, it is even more important to provide gamma cor- 
rection by electrical circuit design. Use of the negative picture allows 
direct photography on positive stock resulting in both increased speed 
and reduced cost. 

We found it desirable to utilize a 12-inch cathode-ray tube operated 
at 25,000 volts. Because of the large aperture of the lens, it is cus- 
tomary to scan an area of only 6X8 inches on the face of this large 
tube in order that the full rectangle of the picture be substantially 
flat and be exposed to the camera without any cutting of the corners, 
thus keeping good focus both electrically and optically. 

Fig. 2 shows a timing diagram which illustrates the phase and 
frequency relationships between the television signals and the re- 
cording camera. At the top line is a timing indication expressed in 
intervals of YISO second. This interval is a subdivision of both the 
30-frame-per-second television-picture interval and the 24-frame-per- 
second film-picture interval. The next line indicates the television 
blanking interval and the useful television-picture interval. The 
actual picture signals and horizontal synchronizing signals occur in 
the interval entitled "scan" in the second line. Here the television 
field interval of VGO second provides half of the interlace picture, and 
the succeeding Veo-second field interval provides the other half of 
the television interlace. Accordingly, two fields of television scan- 
ning vertically from top to bottom constitute one complete frame 
of television picture in an elapsed time of Vso second. On the next 
line there is shown the camera-shutter characteristic which must 
be very carefully adjusted for proper interval. On the bottom line 
the pulldown cycle is illustrated. The most critical characteristic 
in the recording camera is the timing of the shutter blanking and 
exposure interval. The absolute intervals are the most important, 
and if they are appropriately adjusted, then the exact phase 
relationship is not very critical. As shown in Fig. 2, the phase 
relationship has been so adjusted that one of the lap-dissolve points 
for opening and closing of the shutter has been tucked under the 



110 



GOLDSMITH AND MILHOLLAND 



August 



television blanking interval. However, the other lap-dissolve point 
is shown approximately in the middle of the television field interval. 
If this shutter is not adjusted correctly, then a bar of distortion is 
likely to appear in the recorded film picture. Such a lap-dissolve 
bar is noticeable as a flicker caused either by underexposure or over- 
exposure on a few elements or lines of the picture. 

It is customary to drive a recording camera by synchronous motor, 
and where the television signal and the recording camera power are 
both controlled by the same power mains, then the camera runs in 
exact synchronism with the television synchronizing generator. 
However, it is desirable in many cases to record programs in one state 



TIME 

( SECONDS! 



120 ifo i?0 '?0 l?0 '20 

I I I I I I 



I I I I I 



ELEVISION ft-* 3 * -0 nTK 

" L ::r G ooo E vc, 

SCAM.NG II.NTTR^cll.NTER^Ctll 



SHUTTER 

PULSE 



FILM 

PULL DOWN / U 



n 



n 



Fig. 2 Television-transcription-camera timing diagram. 

which have originated in another state, thus not necessarily involving 
synchronized power lines. Many films which we have taken have 
been recorded in the nonsynchronous manner, and thus it is highly 
desirable that the shutter angles be appropriately adjusted so that 
the lap-dissolve bars are eliminated. It is best to have a slight 
double exposure on the lap-dissolve lines rather than an underex- 
posure in order that the distortion be minimized. 

On nonsynchronous power supplies the two regions of lap dissolve 
are in slow motion up or down the picture at the rate of the difference 
frequency between the 60-cycle supply controlling the synchronizing 
generator and the 60-cycle supply driving the synchronous motor of 
the field camera. Two such bars are present as seen in Fig. 2. 

The camera shown in Fig. 1 uses 16-mm film and can employ a reel 
having 1200 feet of stock thus allowing about 33 minutes of recording. 



1948 



TELEVISION TRANSCRIPTION BY FILM 



111 



In practice, a dual system is employed so as to record programs for an 
indefinite period. The teletranscriptions may be used for rebroad- 
cast, promotional advertising, criticism of program techniques and 
content, and legal records. 

Fig. 3 is a picture which illustrates some of the work that can be 
done by recording from television. This is an original enlarged from a 
frame of 35-mm motion picture film. Fig. 4 is a recorded television 
transmission of the same scene. Fig. 5 is another original, of which 
Fig. 6 is the television recording. These were not taken on a 16- 
mm camera and do not indicate any of the banding. 

Another very promising use of transcriptions is for theater tele- 
vision. The equipment and films discussed here have been primarily 
for use on 16-mm film, but the same principles apply to the project of 
theater television, using 35-mm film and a process of rapid develop- 








Fig. 3 Original. 



Fig. 4 Photograph received 
cathode-ray tube. 



on 



ment for immediate projection in a minute or less after reception. 
Much thought is being given to the theater-television possibilities and 
systems are being studied having other than the standard broadcast- 
line and frame rates. However, the immediate demand for recorded 
television programs is so great that the 16-mm equipment here 
described has been developed to a practical degree and is in active use. 
Television networks eventually will rely upon radio relay or coaxial 
cable to connect the various stations. However, until such facilities 
can be provided and can be operated at a reasonable cost, it is possible 
for the network syndication to be accomplished by television tran- 
scriptions, recording the major programs in the originating stations 
on film which may then be shipped to the subscribing affiliates. 
Where this method is employed the recording-camera equipment will 
employ a separate sound system for best quality, since there is time 






112 GOLDSMITH AND MILHOLLAND August 

for limited editing and time for the special processing of the two films 
in preparation of the prints. 

On the other hand, for some applications such as a documentary 
record of transmission, which eventually might be required by the 
Federal Communications Commission it is entirely adequate to em- 
ploy a single sound camera whereby the general subject matter and 
sound are recorded on a single film. Here it is probable that no 
prints would be required, and therefore greatest economy should be 
practiced. However, for rebroadcast the highest possible quality 
of sight and sound is desired and a separate sound system is preferred. 

For some forms of recording the picture may be photographed on 
to negative stock as a negative picture. Then, a television system 




Fig. 5 Original. Fig. 6 Photograph received on 

cathode-ray tube. , 

may be employed for viewing this picture since we have a regular 
means of reversing the picture polarity electrically in the television 
chain. We have used this method in regular broadcasts to save time 
in film processing, taking regular newsreel records on the original 
negative and playing the negative film through the television film 
camera, reversing the video polarity so as to transmit a positive picture. 
Now a word about future possibilities with television transcription. 
Already the sensitivity of television cameras using the image-orthicon 
tube exceeds the sensitivity of most photographic emulsions. Thus, 
we can say that the television-camera chain serves as a light amplifier, 
extending the range of photographic recording to scenes having lower 
lighting levels than can be successfully recorded by a film camera 
alone. However, further development must occur before the sensitive 



1948 TELEVISION TRANSCRIPTION BY FILM 113 

television system can fully match the contrast gradation fidelity and 
resolution and sharpness available by direct film camera methods. 

The intermediate film technique has already developed to such a 
degree that the transcription compares favorably with an original 
film used as the subject matter for such a transcription. 

The television camera promises excellent utility in a motion picture 
recording studio. At present such a camera is primarily an aid to 
the regular picture recording camera. Used as such, it gives the 
Operations Personnel a means of seeing immediately the setup and 
programming for the scenes, thus providing a control far more useful 
than the customary waiting until development of the film can provide 
for a means of analysis of what is being filmed. 

Usually such a viewing takes place the day after the scene has been 
photographed ; this unnecessary delay proves very expensive. The 
television camera used in conjunction with the motion picture camera 
can provide at once on television monitors the scenes being recorded. 

Ultimately it may well be that the television camera head alone 
may be used in the studio to pick up the scene and the complex film 
equipment will be located in central permanent laboratories where 
both sight and sound are recorded. This procedure of placing micro- 
phones in the studio and the complex sound-recording equipment in 
the laboratory is customary at present in many studios. It is entirely 
possible that both the sound and the picture recording equipment 
may be located in the central laboratories. In this way the scenes 
can be monitored while they are being recorded, thus aiding the 
co-ordination between directors, cameramen, and performers. 

DISCUSSION 

MR. J. G. BRADLEY: I am interested in the recording aspect of this because I 
see in this recording a possibility of creating and preserving records as library 
material. What losses do you sustain when you retelevise these pictures taken 
by camera from a televised image? In other words, how does the retelevised 
picture compare with the original televised image in sound and picture quality? 

DR. T. T. GOLDSMITH, JR. : The film recording compares favorably with the 
original televised image. The sound was degraded pretty much tonight. This 
sound was dubbed in from various sources. The camera that you see here does 
not have sound facilities with it. The sound, for example, on the President's mess- 
age was recorded in New Jersey in my house, and the picture was recorded here 
in New York, and the President was speaking in Washington. So it was a rather 
peculiar combination which resulted in the film you have seen. Other parts of the 
sound here were dubbed from other recordings. 

We are putting together complete sound-and-picture recording apparatus all 
under one control, where we expect the sound quality to be quite comparable to 
the reproduction obtained over the radio channel by direct reception. 



114 GOLDSMITH AND MILHOLLAND August 

As to the picture quality, which I believe is a primary consideration that 'you 
have, we have rebroadcast quite a number of the programs which were recorded in 
this manner. We know there are many flaws left in this system. We know there 
are many cures for some of the flaws. Some of them will, inevitably, degrade 
the picture somewhat. However, even at the present status, we have had things 
working as we want them for film recording. Then we have played over the air a 
test film consisting of a section of 16-mm film and then a section of teletranscribed 
film. It was very difficult to tell at the receiving point just where one stopped and 
the other started. 

There is a noticeable difference particularly for those who are looking for the 
flaws and the bars that are present, but teletranscription does give you a quite 
faithful recording of what is going on the air. I think the Eastman people will 
agree with me that many of the tests we have made have recorded just about all 
there is on the cathode-ray tube. Some of the films that you have seen tonight 
were taken with mobile field equipment, which does not have the full resolution 
and the resulting characteristics of the iconoscope cameras. Some of the shots 
were recorded from iconoscope-camera signals, and they are better. However, 
even those suffer from lack of depth of focus in the studio. The iconoscope is not 
too sensitive. So we have to use a fairly large aperture lens on the pickup icono- 
scope camera. As a result, the background is badly defocused, but we have means 
under development for eliminating that characteristic and having good resolution 
and at the same time good depth of focus in the studio equipment. Thus we 
shall have something that can realize more nearly a full 525-line television system. 

Obviously, you cannot go to much better resolution than that and still keep 
the broadcast standards that we have today; but I do believe for many docu- 
mentary records the 16-mm film recorded by television can compare very favor- 
ably with 16-mm direct recordings, and certainly be equal to the average record- 
ngs used for film work generally. 

MR. BRADLEY: I think my question is more technical than the way you have 
answered it. In preserving motion picture records, we have to look forward to 
copying the film. Each time we copy it we lose some light, whether it is 5 per cent 
or 10 per cent, but there is a limit to the number of times we can copy a motion 
picture, until there is complete degradation of light. Suppose you televised a mo- 
tion picture and copied it with a camera. Then you televise the copied picture 
and copy it again. How many copyings can you get before this degradation? 

DR. GOLDSMITH: There is a small degradation each time. Do you mean the 
degradation by retelevising, or by printing a. lot of positives from one negative? 

MR. BRADLEY: Degradation by rephotographing the televised image. I 
understand you can televise a picture many times without any degradation, 
but when you photograph it again from a television screen, what degradation 
sets in there? 

DR. GOLDSMITH: There will be some further loss, of course, because each time 
you televise it you change the contrast fidelity a little, and that would penalize it. 
However, I do not know just what conditions you would encounter that would 
make it necessary to transcribe again and again, for example, down to the tenth 
transcription. If you transcribe once to get the film record down permanently 
on a first negative, then you can make positive prints in any number, with the 
normal limitation of printing, 'distribute them that way, and thereby, say, have 



1948 TELEVISION TRANSCRIPTION BY FILM 115 

50 positive prints going out to 50 affiliated stations, each one suffering only one 
degradation due to retransmission. 

MR. COOK: I noticed in the presentation of the last motion pictures 
that there was less disturbance of the picture than in any of the previous ones, 
either the projected demonstration tonight or the pictures that Captain West had 
the other night; in other words, the picture was extremely stable. Were these 
broadcast or were these taken directly from a coaxial cable to your tube? 

DR. GOLDSMITH: We have done both. If I remember these particular clips 
that were put together here, most of these were done at the station, but many of 
them were by radio-relay link; not many of them, but many that we have done 
have been that way; for example, the baseball game came over by radio-relay 
link on some of its paths. Of course, the President came from Washington to 
New York on the 2.7-megacycle band with coaxial cable. There were various 
transmission means employed on many of the shots that you saw tonight. Some 
of the others were taken off what we call a studio line right from the studio 
without any broadcast interference. The quality that you saw here is quite repre- 
sentative of what you get in many good receiving locations around New York, 
which is perhaps 50 per cent of the locations that have television sets. 

MR. BLOOM: You mentioned you had difficulty with the power-line 
frequencies being different at one point of transmission than at the point of re- 
ceiving. Is it possible to use a synchronizing system, an automatic-frequency 
system, to drive your synchronous motors to operate that? 

DR. GOLDSMITH: We have done that. On some tests we have driven our power 
equipment from a synchronous supply operated that way, but we feel that if we 
can get this shutter phasing and shutter angle appropriate, particularly the 
shutter angle, then it will be unnecessary to take that precaution, and it is a far 
simpler set of equipment. You can run completely synchronous with the trans- 
mitted signals by using a synchronizing process of vertical field control to lock 
in your mechanical mechanism as well. 

MR. HUGH CHAIN: Are you offering this commercially yet? Is it out of the 
experimental stage? If it is, have you any idea of the rates for this service? 

DR. GOLDSMITH: It is a little premature. We are building the units. We built 
quite a few of them experimentally and we are getting the things into production, 
but one of the major problems has been the commercial camera: The commer- 
cial electronic equipment is pretty well along, too. The general plan, so far as we 
know, is to sell these units to interested subscribers, primarily thinking that 
the first people that would want them would be broadcast stations to use for regu- 
lar transcription at the broadcast stations. The units are available. 

MR. CHAIN: But are you offering the scripts and transcription service to ad- 
vertisers to your stations? 

DR. GOLDSMITH: Yes, that has been done for some time. We have been re- 
cording programs for sale to advertising agencies, and so forth. 

MR. CHAIN: Mr. Feldman, the Jack Kilty part of the transcription did not 
seem to have high contrast. You mentioned to me that it was done on sound 
positive film. Is that lack of contrast inherent in the film, or what was the situ- 
ation there? 

MR. W. FELDMAN: We have used a couple of different types of sound positive 
films. As to the particular one of the Jack Kilty Show, it was on 5302. 



116 GOLDSMITH AND MILHOLLAND 

MB. ROBERT FRASER: That film was a work print, a very hasty print. As 
soon as we saw the banding, we did not go any farther. So the quality is very 
poor. However, the negative would be capable of a much better print. 

MR. FELDMAN: Actually, this print was made up specifically to show banding, 
and not for any picture quality. That was not the prime purpose. 

MR. LEWIN: There was a statement made by Dr. Maloff that confused 
me quite a bit, and I did not have an opportunity to question him at the time. I 
wonder whether one of the authorities in television would help to clarify it. 

Dr. Maloff said that in counting the number of lines the television engineer 
counts both the black and the white lines. I have always been under the im- 
pression that when you say there are 525 lines, you mean the electron beam 
actually scans 525 lines in the 30th of a second. That would be 525 white lines. 
Am I wrong in that or not? 

CHAIRMAN PAUL J. LARSEN : That is correct. 

MR. LEWIN: In other words, if you count the black and white lines, there 
are 1050 lines. 

DR. GOLDSMITH: I shall try to clarify that in this way: In television we use 
scanning lines which are potentially either white or black, or some gray inter- 
mediate tone, depending upon the signal that is being produced. In the motion 
picture terminology of lines, they refer to a series of black lines ruled on a paper 
with equally spaced white lines between. 

In television it is true that if you look at a television picture you can see the 
scanning lines in the high-light part of the picture as white strips of light across, 
with a very thin space between that may be black. We try in television to make 
that space as small as possible; in other words, the spot size is just the size of the 
space between the centers of two lines, in the interlace system. So that the lines 
that are white just merge with one another on their edges. 

Theoretically, in a perfectly square spot-scanning system in television you have 
no black lines in between, and there comes a difference between the motion pic- 
ture terminology of black lines separated by white spaces and the television sys- 
tem where the scanning processes, as to lines, can either be black or white or gray, 
at the control of the grid in the cathode-ray tube. 

MR. DAVID B. JOY: I understood the speaker to say that by using a 35-mm 
camera, a picture could be taken of the television image, developed, and ready for 
projection in the regular projection equipment of the theater within a few min- 
utes after the picture was received, thus giving you as much light on your projec- 
tion screen as you would get with an ordinary motion picture. If that equipment 
is not too complicated, it might be one solution to the theater television. 

DR. GOLDSMITH: That is right. It is not too complicated; in fact, that 
few minutes that you talk about has been experimentally pulled down to less than 
a one-minute delay. A film frame is exposed in front of the transmitted picture 
at the cathode-ray tube, is run through a developing machine, having both de- 
veloping and fixing, at high temperatures and high drying speeds, and threads 
right on through into the projector in the theater and can be projected in that 
manner. The equipment is rather complex in the developing and fixing process. 
I do not know about the permanency of such records, but it does allow editing, 
saving the film if you want to for longer times, or allowing almost instantaneity of 
broadcast, almost as soon as received. 



Television Recording Camera* 

BY J. L. BOON, W. FELDMAN, AND J. STOIBER 
EASTMAN KODAK COMPANY, ROCHESTER, NEW YORK 

Summary A 16-mm motion picture camera for recording television pro- 
grams at sound speed from a monitor receiving tube is described. Basic 
camera-design features include a 1200-foot magazine, which permits con- 
tinuous recording of a half-hour program, separate synchronous-motor drives 
for the shutter and film-transport mechanisms, an 8-tooth sprocket pulldown 
actuated by an accelerated geneva star, an //1. 6, 2-inch focal length coated 
lens, and a 72-degree shutter. Other features include a " bloop" light to pro- 
vide registration with the sound-film recorder, a film loop-loss indicator, and 
appropriate footage indicators. 

Some general operating characteristics of the camera are included along 
with a description of the pulldown system and the general problem of film 
steadiness. The last is particularly critical because of the high accelerations 
involved in the pulldown, in addition to the reaction of film to temperature 
and humidity changes. 

IN THE RECORDING of television-tube imagery on film, one is con- 
fronted with the primary problem of reducing an image frequency 
of 30 cycles per second on the tube to one of 24 cycles per second on 
film. It is possible to record television images satisfactorily at 15 
cycles per second or even at 7 1 /* cycles per second. In conforming 
with the standards of the American Standards Association of re- 
cording sound on film, however, one is limited to a frequency of 24 
frames per second. Since the ratio of the two frequencies is 5 : 4, it is 
evident that the transition is most easily accomplished by omitting 
one of every five scanning traces. More exactly, the following se- 
quence of events occurs: With the camera and television tube syn- 
chronized, film is exposed for one complete tube cycle, lace, and inter- 
lace patterns. During the first quarter of the next complete cycle 
the film is advanced one frame. Exposure takes place for the remain- 
ing three quarters of this cycle and the first quarter of the next cycle, 
after which the film is again advanced. Fig. 1 shows an exterior view 
of the camera and in Fig. 2 may be seen the schematic representation 
of the events. 

As a direct consequence of the limited pulldown time indicated 
above, the camera is restricted to a closed-shutter angle of 72 degrees. 
In addition, the pulldown angle for the film must be less than 72 
degrees by the angle which the aperture subtends. 

* Presented October 23, 1947, at the SMPE Convention in New York. 

AUGUST, 1948 JOURNAL OF THE SMPE VOLUME 51 117 



118 



BOON, FELDMAN; AND STOIBER 



August 



In our camera the pulldown action is accomplished by means of an 
8-tooth sprocket which is indexed by an 8-point geneva star. It may 
be readily seen from the geometry of the star and its driver that the 
latter must rotate 135 degrees during the indexing operation. But 
since this angle is greater than the permissible pulldown angle, it is 
necessary to interpose an accelerating mechanism between the con- 
stant-speed drive shaft and the geneva star. A variable-arm, spline- 
and-slot movement, shown in Fig. 3 and treated mathematically in 
the Appendix, is used to reduce the pulldown time from one which is 

equivalent to 135 degrees to one 
which approximates 57 degrees. 
The effect of this accelerator is 
to produce extremely large peak 
film accelerations. As an ex- 
ample, the peak acceleration 
shown in Fig. 4, for operation at 
24 revolutions per second, pro- 
duces a linear film acceleration of 
the order of 6 X 10 4 inches per 
second. A standard 8-point ge- 
neva star driven by a constant- 
speed shaft at the same speed 
reaches about one tenth the 
above acceleration at its peak. 
As may be expected, a large 
force is produced on the inter- 
mittent movement. In addition, 
such problems as optimum pres- 
sure-pad tension, film steadiness 
in the gate, and a general increase 
in noise level become more evident. In view of the large forces pro- 
duced, it was deemed advisable to use a sprocket pulldown instead of 
a claw since the life of the latter would not be long enough for the 
heavy-duty operation required. 

FILM STEADINESS 

During the preliminary camera tests it was observed that film 
steadiness was very erratic and was particularly dependent upon hu- 
midity conditions. As the relative humidity reached 85 per cent or 
higher, it was impossible to obtain any semblance of picture steadiness. 




Fig. 1 Exterior view of camera. 



1948 



TELEVISION .RECORDING CAMERA 



119 



This general effect is not new and has been attributed to an adhe- 
sive action between the film and the gate and pressure pad, some- 
what analogous to the behavior of two polished glass surfaces in con- 
tact and moved parallel to each other. Since the ratio of static to 
kinetic friction is large, the forces required to start the motion and con- 
tinue it vary considerably. It was noted that so far as the film was 
concerned, consideration had to be given to both surfaces, the base as 
well as the emulsion. As a consequence, both the gate and pressure- 
pad constructions were modified. Instead of permitting the film to 
ride on a continuous track in the gate, six studs, three on each side, 
were embedded in the tracks and then lapped so that the stud sur- 
faces were three or four thousandths of an inch above the track sur- 
face. The studs not only served to decrease the contact area between 



STANDARD 
'(1/60 ~SEC) 



CAMERA FRAME 



STANDARDT FRAME 



DOWN 



Fig. 2 Timing cycle of television monitor and camera. 

the gate and film, but also reduced emulsion pile-up and its attendant 
effect on steadiness. It should be mentioned, in passing, that a 
straight gate and pressure pad are being used. 

Modifications made on the pressure pad consisted in replacing the 
usual type of continuous chrome-plated track with a 6-studded track 
which matched the studs in the gate. In addition, another pressure 
pad constructed solely of nylon and with continuous tracks was used. 
Both pads provided steady film registration. It was observed, how- 
ever, that the former permitted the film to buckle slightly and so was 
discarded in favor of the latter. To date, no life tests have been made 
on the nylon, although no physical changes have been noted after 
some 25,000 feet of film have been run through the camera. It is 
anticipated that the nylon will provide satisfactory operation and a 
reasonably long life. 



120 BOON, FELDMAN, AND STOIBER August 

GENERAL PROPERTIES 

Two synchronous motors are used to drive the camera. One is used 
solely for the purpose of driving the shutter, and the second one, a 
larger motor, takes care of the entire film transport. It was felt- 
necessary to isolate the two systems in order to prevent any "hunt- 
ing" from affecting the shutter. A coupling which ties the two motor 
shafts together permits continuous observation of synchronization. 
Once this coupling is set, it should not be necessary to readjust the 
two motor positions, since their operation will remain synchronized. 

The importance of a separate motor drive for the shutter is evident 
when one considers that it is necessary, on alternate exposure frames, 
to record from the middle of one scanning trace, as shown in Fig. 1, 



LOCUS OF SLOT MOTION 



GENEVA DRIVE PIN 




\ 

\3ENEVA 

Fig. 3 Slot-and-spline driving geneva. 

and to complete the full cycle on the first half of the third scanning 
trace. Unless the shutter is able to reproduce its action, the scanning 
lines show up as not meeting or overlapping. The net effect is a type 
of banding which is reproduced on the film as an alternately varying 
density region. It is not anticipated that one will be able to synchro- 
nize shutter operation so that recording takes place at precisely the 
same position on alternate frames. It should be possible, however, to 
reduce the banding to, say, one scanning line. In tests made at both 
the National Broadcasting Company and Du Mont Studios, it was ob- 
served oftentimes that it was possible to record with no trace of 
banding. On other occasions, a form of banding, which resulted from 
shutter unsteadiness or from shifting scanning lines, took place. 

A 1200-foot, double-chamber magazine is supplied with the camera 
and is a self-contained unit in that it permits housing both the un- 
exposed and the exposed filrn and may be readily removed from the 



1948 



TELEVISION RECORDING CAMERA 



121 



camera. The take-up drive consists of a sprocket-and-chain move- 
ment, which is driven from a clutch-controlled shaft on the camera 
proper. Separate arms are used to guide the film on both the supply 
and take-up sides of the magazine chamber. Appropriate light locks 
are provided to permit changing of loaded magazines in a lighted room. 
It was mentioned above that some difficulty in film steadiness in the 
gate was encountered. In tests made on the pulldown sprocket, it 
was noted that there was a need not only for a "snubbing" roller, but 
also a stripper roller which would aid in stripping the film from the 




DRIVE SHAFT ROTATION 



Fig. 4 Acceleration curve for 57-degree ac- 
celerated pulldown. 

pulldown sprocket. The former was located in a position approxi- 
mately three frames from the edge of the aperture, although it was ob- 
served that within plus or minus 10 degrees its position was not too 
critical. The stripper roller was located below the sprocket and in 
such a position as to aid the film in following its natural stripping path. 
Several tests were made in an effort to determine the optimum pull- 
down sprocket diameter. However, since there seemed to be little 
difference in their operation, a final choice was made of a 0.762-inch 
diameter sprocket. 

One other property which has been mentioned is the operation 
noise level of the camera. The high accelerations which take place 
in the pulldown mechanism, as well as the gear-reduction drives which 



122 



BOON, FELDMAN, AND STOIBER 



August 



ate used, all contribute to camera noise. The level is not high enough, 
however, to be objectionable. 

ACKNOWLEDGMENTS 

Considerable credit and thanks are due to the technical staffs of 
both the Allen B. Du Mont Studio, Station WABD, and the National 
Broadcasting Company Studio, Station WNBT, We are especially 
grateful for their many suggestions which have been offered and in- 
corporated in the preliminary camera model and also for their con- 
tinual assistance in providing studio time and facilities for the pur- 
poses of testing the camera. 




Fig. 5 Eight-point geneva geometry. 

APPENDIX I 

Motion of Eight-Point Geneva Star 

In Fig. 5 is shown the geometrical arrangement of the intermittent 
geneva star with center at P and the driving pin with center at 0'. 
Since we require that the driver move the star 45 degrees during its 
period of engagement, certain well-defined relations are determined. 
From the figure, 

R = Ri tan 22.5 degrees (1) 

x = R (1 - cos 6) (2) 

where x is the horizontal component of displacement, R the distance 
from 0' to the center of the driving pin, and 6 the angle of rotation of 
the driving pin. Also, 

R! - y = R sin 6, (3) 

whence R cot 22.5 degrees - y = R sin 6, (4) 



1948 TELEVISION RECORDING CAMERA 123 

and y = #(2.41 - sin 0). (5) 

Thus, ^ = tan <p = 2.41"- si n ^ 

where v is the angle of rotation of the star. We have taken the origin 
of motion at the initial point of engagement of the driving pin with 
the star, but it turns out to be more useful if the origin is selected co- 
incident with the maximum position of engagement of the star and pin. 
Consequently, the shift in origin changes (6) to 

t^^-^r-^f/M) (7) 

where A is an arbitrary phase angle. We shall later take it to be 67*/2 
degrees, consistent with the requhements stated above. Solving for 
<p we obtain 

- cos (A + 0) 



r 1 - c 
|_2.41- 



sin(A 



(8) 



We shall now obtain the relations between the angular velocity and 
acceleration of the pin and star. The first derivative with respect to 

time yields 

. = 2.41 sin (A +0) H-cosCA + 0) - 1 , 
7.82 - 4.82 sin (A + 0) - 2 cos (A + 0) 

which reduces to 

(cos A + 2.41 sin A} cos -f (2.41 cos A sin A) sin 1 
^ ~ 7.82- (2 cos A + 4.82 sin A} cos + (4.82 cos A -2 sin A) sin 



and which, for A = 67*/2 degrees, becomes 

2.61 cos - 1 . 
* " 7.82 - 5.22 cos 



(11) 



The angular acceleration of the star is obtained by a second time 
differentiation. 

. (7.82 - 5.22 cos 0) (-2.61 sin 0) - (2.61 cos 0-1) (5.22 sin 0) , a 

(7.82 -5.22 cos 0) 2 
2.61COS0-1 .. 
r (7.82 -5.22 cos 0) 



which reduces to 

15. 18 sin 2.61 cos 1 



(7.82 - 5.22 cos 0) 2 ' (7.82 - 5.22 cos 0) 



e. (13) 



If the driver were moving at constant velocity, the second term in 
(13) would vanish. Since, however, we shall be considering a system 



124 BOON, FELDMAN, AND STOIBER August 

where the driving pin is not moving with constant velocity, the second 
term will be of significant importance. 

APPENDIX II 
Spline-and-Slot Accelerating System 

At a fixed distance Rz in Fig. 6, about A as center, we drive a slot at 
constant speed. The slot engages a spline whose driving center is at 
0' and is tightly coupled to the geneva drive pin. An angle of ro- 
tation a. in the constant drive produces a rotation 6 in the output. 




LOCUS OF SLOT MOTION 



\ SPLINE 



Fig. 6 Slot-and-spline geometry. 

From the law of sines we obtain 

-^ = -^ in triangle AOB'. (14) 

sin a sm 

Also C 2 = (R t + 6) 2 + R 2 * - 2R 2 (R, + 6) cos a. (15) 

But (#1 + &) = (R* ~ a), 

whence C 2 = (R 2 - a) 2 + R 2 * - 2R 2 (R 2 - a) cos a. ^ (16) 

From (14) and (16) we have 

. fi _ _ Rz sin a _ x 17 ^ 

= {(#2 - a) 2 + RJ - 2R*(R* - a) cos a} 1 /*' 

R 2 sin a 



tan " * 



fi, cos a - (ft - a)' 



and cot. = T'-. (18) 

Rz sm a 



1948 TELEVISION RECORDING CAMERA 125 

Equation (18) provides the necessary relation between 6 and a, i.e., 
the output and input angles of rotation. Once Rz and a are selected, 
one has a well-defined relation for the two angles. The zero point of 
operation of the system has been taken with the slot engaging the 
spline at the closest distance of approach to 0'. 
From (18) we have 



= cot- 1 foot a. - (l - -j~\ csc "]. (19) 



The first derivative with respect to time provides us with an angular 
velocity relation ; namely, 

1 _ (l ) C o S 

RJ a. (20) 




-[(*-!)- 0-t)> * 
-i) 1 -'('-*)"]' 



To obtain the angular acceleration relation we differentiate a sec- 
ond time, noting that a is a constant, and obtain 



(21) 



From (11) in Appendix I we obtain the geneva velocity as a function 
of its input drive. But the input drive of the geneva is governed by 
the output of the pin-and-slot drive since the two are coupled. Thus, 
we are able to treat the geneva motion in terms of the constant-ve- 
locity drive. Given 

2.61 cos 9 - 1 , 
* ~ 7.82 -5.22 cos/ 

and replacing by (20) we obtain 

2.61 cos - v > ^ (23) 

* 7.82 - 5.22 cos 0\ ' -^ ~ < "' (Z6) 



Substituting for cos 6 in terms of a gives 

2.61 [Rt cos a - (Rt - a)] - Z 
7.82Z - 5.22[# 2 cos - (R 2 - a)} 




a (24) 



126 



BOON, FELDMAN, AND STOIBER 



where 



= \/2(# 2 2 - 2R 2 a) (1 - cos ) + a 2 . 



In a similar manner we may obtain the angular acceleration equa- 
tion of the geneva in terms of the constant-speed shaft rotation. 
From (13) in Appendix I we have 

15.18 sin e 2.61 cos 6 - 1 



where 



(7.82 - 5.22 cos 0) 2 

>-('-*) 



(7.82 - 5.22 cos e) 



(25) 




COS a 



-[('-!;) -('- 



cos e 



and sin e 




cos a (R z a) 



sin a. 



Performing the indicated replacements in (25), we obtain 

.. _ [" -15. 187^2^ sin a "I 

*' = U7.82Z - 522(R 2 cos a - (R* - a)] } 2 J 



X 



1 ~ ( l ~ l) COS " 



(26) 



_ f 2.61 [R 2 cos a - (Hz - a)} - Z "I 
U7.82Z - 5.22[ 2 cos a - (R 2 - a)] }J 




The appropriate constants foi a 57-degree pulldown angle have 
been substituted in the final equation and one half of the symmetrical 
acceleration curve of the geneva plotted in Fig. 3. For ease of ob- 
servation, the curve has been inverted and shifted from its true posi- 
tion on the other side of the zero line. 



Development of Theater Television 
in England* 

BY A. G. D. WEST 

DIRECTOR, CINEMA-TELEVISION, LTD., LONDON, ENGLAND 

Summary This paper will give a historical review of the progress of theater 
television projection in Great Britain, both before and after the war, and will 
describe the design and performance of the equipment which has been de- 
veloped for distribution and projection of television programs. It will also 
indicate the proposals now being made for the setting up of a theater tele- 
vision service in England, first in London, and then throughout the country. 

I. INTRODUCTION 

THE ENGLISH cinema exhibitor is somewhat bewildered regarding 
the subject of television and how it will affect him in the future. 
Previous to the war, certain cinemas had large-screen television equip- 
ment installed where programs of a topical nature transmitted by the 
British Broadcasting Corporation were reproduced on the screen to 
paying audiences. Results achieved indicated that with the normal 
course of technical progress, television projection could, in time, pro- 
vide a picture equal in quality to that given by normal film projec- 
tion. But the practical problem of the use of television for cinema 
entertainment, particularly in respect to how programs could be 
built using the television medium, was the subject of much conjec- 
ture, and sufficient experience was not available then, nor is it even 
now, to enable the exhibitor to obtain a clear view as to how such 
entertainment would be organized and presented to the public. I 
have spent some time trying to get the entertainment industry to 
study the practical problems concerned with the successful utilization 
of television in its applications to the cinema industry. I have spent 
much more time, naturally, endeavoring to press forward with the 
solution of the technical problems, holding the view that, in the 
achievement of an acceptable technical result, the technician will have 
carried out his part of the bargain; it may be that as this state of 
technical perfection is more closely approached the clarification of the 
program requirement will be accelerated, and we shall find the means 
of revitalizing the cinema industry in a way which will be a source of 

* Presented October 21, 1947, at the SMPE Convention in New York. 

AUGUST, 1948 JOURNAL OF THE SMPE VOLUME 51 127 



128 WEST August 

satisfaction to both technician and exhibitor. Large-screen tele- 
vision has provided a means of interesting and attracting the cinema 
patron on certain special occasions. On the other hand, we are not 
yet satisfied that, either technically or in respect to program value, we 
can yet retain the permanent interest of the public. We are only 
part of the way through our job. Let us, therefore, take stock of the 
present situation, and obtain clarification on some of our problems, 
and how best to attack them. 

In the advent of a new art this was exemplified when sound, aris- 
ing out of broadcasting, was applied to cinema technique we must 
find how the new art can help existing practice and vice versa. Our 
chief problem today in the cinema industry is to study how tele- 
vision can help the cinema, and also how the cinema can help tele- 
vision. This is the vital moment, when television is just beginning 
to show its head, for the cinema industry to take into account in its 
planning for the future, both technically and commercially, the in- 
valuable aid which television can provide in the field of theater enter- 
tainment. Television enthusiasts (we shall call them "tele-vision- 
aries") who have made a close study of the commercial possibilities of 
the use of television for the entertainment of cinema audiences, have 
forecast that, provided a broad co-operative view is taken by all the 
various entertainment interests, including those which promote sport- 
ing and similar events, opportunities for expansion in the entertain- 
ment industry can be considerable, and would fully justify the wildest 
dreams of the most imaginative exploiters in the entertainment field. 

The following observations aim at giving a review of the position 
of theater television in Britain^ and a summary of the aims of the 
technician in preparing for full commercial use large-screen television 
equipment, and the means whereby programs can be provided for 
such an equipment, together with a statement of the various aspects 
which will need to be considered in detail by the exhibitor, between 
now and such time when commercial equipment will be available on 
the market. The paper is concerned only with black-and-white pro- 
jection. We have nothing as yet to show on color. 

II. REVIEW OF PROGRESS UP TO 1939 
Early History of Large-Screen Projection 

Up to the beginning of the war in 1939, home and theater television 
progressed side by side during those prewar years ; therefore, a few 
words should be said on the development of the home television service. 



1948 . THEATER TELEVISION IN ENGLAND 129 

The beginning of official transmission of television in England was 
due to the dogged persistence of John Logie Baird, who, as a result 
of his experiments and demonstrations, over the period from 1923 to 
1928, was able to get the British Broadcasting Corporation to radiate 
vision signals, first in 1929 by an experimental service, and later, from 
August, 1932, in the form of a regular program service. These televi- 
sion transmissions provided over the normal broadcast channels a low- 
definition picture on a 30-line basis. Such a coarse texture of picture 
rendered the transmission of small detail impossible, and the program, 
although interesting, had little entertainment value. But it started 
the ball rolling, and, as you well know, from 1933 onward work was 
commenced in many laboratories in England, America, France, and 
Germany, toward the development of a higher standard of definition. 

The low-definition broadcast service ceased in September, 1935, and 
its place was taken by regular transmissions from the new television 
station at the Alexandra Palace, London, on a 405-line interlaced 
standard developed by the Marconi and Electrical and Musical In- 
dustries companies. 

Home and Theater Television 

During the three years from August, 1936, to September, 1939, 
some 20,000 home television receivers were sold in the London area; 
the majority of these incorporated direct- viewing cathode-ray tubes 
with a picture size between 8X6 inches and 13 X 10 inches. 

During this period there was very rapid development in the type 
of program material. Not only was studio space at Alexandra Palace 
considerably enlarged to allow a variety of studio programs to be 
transmitted, including plays and variety (vaudeville) productions, 
which involved the use of multistudio technique, but the range of 
outside events was increased by the laying of a ring cable of the co- 
axial type, connecting the more important points of entertainment 
and interest in the London area, and also by the provision of mobile 
equipment which linked such events as Rugby football matches, on the 
outskirts of London, and the Derby at Epsom Downs 20 miles away, 
with Alexandra Palace, for rebroadcasting from that station. 

The hours of transmission for home screens averaged 18 hours a 
week, usually one hour in the afternoon and two in the evening, and 
the improvement in programs, particularly in respect to outside 
broadcasts and actualities (such as cricket, tennis, and boxing matches) 
was so considerable in 1938 and 1939 that the home televiewer had 



130 



WEST 



August 



exceedingly good entertainment. (Figs. 1 and 2.) So far the 
London area was the only favored area, but plans were in hand 
for the extension of the service to other centers of population. How- 
ever, television was brought to an abrupt conclusion in Great Britain 
on September 3, 1939, and from that date onward no transmissions of 
any type took place until the London Television Service was re- 
opened in June, 1946, following the report of the Government Tele- 
vision Committee published in April, 1945, which recommended early 

resumption and expansion of the 
television service in London and 
in the provinces. Contracts have 
been placed for the erection of 
the Birmingham and Manchester 
Stations, which will, in the first 
instance, act mainly as relays of 
the London program. Eventu- 
ally four more provincial stations 
will be built, providing a home 
television service by 1952 which 
will be available to 75 per cent of 
the population of Great Britain. 
As you well know, commercial 
sponsoring of programs, both 
sound and television, is not tol- 
erated, and, therefore, the pro- 
vision of the service, which at 
the moment costs the B.B.C. 
half a million pounds per annum, 
in return for which they receive 
25,000 pounds per annum, being 
one pound per set per annum 
for the 25,000 sets already in 
operation in the London area, does not appear, at the moment, to 
be an economic proposition. But the B.B.C. remains undaunted by 
this problem, looking forward to a reversal of the economic picture, 
when the country is covered with the television service, and when 
there are sufficient material and labor available to manufacture enough 
television receivers, at a reasonable price, -to satisfy all requirements. 
All programs, of course, do not satisfy all tastes, but the B.B.C. is 
doing wonderful pioneer work, considering the limitations of space 




Fig. 1 B.B.C. television cameras at 
the trooping of the color, Horse Guards 
Parade, London. 



1948 THEATER TELEVISION IN ENGLAND 131 

and equipment. I am perfectly satisfied to receive two good pro- 
grams a week, for example, a good play or a good variety show, or a 
good sporting event, for my one pound a year license fee. My satis- 
faction is, of course, subject to the somewhat selfish provision that 
I am not required to look at programs which I do not want to see; 
we are beginning to realize that home television can be a remarkable 
time-waster, if rigid self-control is not exercised in switching "on" or 
rather "off" the receiver. 

The progress of home television in Great Britain has been referred 
to in some detail, because in many respects, and particularly in rela- 
tion to the provision of a program, the service is quite different from 




Fig. 2 B.B.C. television cameras at the Oxford and Cam- 
bridge boat race. 

what you have here and this possibly may indicate slight differences of 
approach to the application of the theater television technique. 

From 1930 onward attention was paid to the possibilities of produc- 
ing television pictures for demonstration to larger audiences. There 
were three main lines of development each of which had a practical 
result: mechanical systems, intermediate film projection systems, 
and cathode-ray-tube projection methods. To these can be added a 
fourth, light-valve systems, which were being thought about without 
yielding anything to indicate possible practical results. 

Large-screen television was first demonstrated to the public in 
Great Britain by John Logie Baird in 1930 at the London Coliseum 
Variety Theater, when he used a screen of 2100 lamps, operated by a 



132 WEST August 

mechanical commutator switch to provide a picture 30 X 70 inches in 
size. This novelty was retained in the theater program for three 
weeks, and, therefore, we are justified in saying that it excited con- 
siderable interest, although the definition was crude, but 'the bright- 
ness was adequate. An extension of this system was demonstrated 
in Berlin by Karolus, who employed a bank of 10,000 lamps arranged 
in a square frame of 100 horizontal rows, each containing 100 lamps. 
These lamps consisted of miniature cathode-ray tubes arranged in 
individual compartments in the screen, and the illumination was pro- 
duced by the excitation of the fluorescent screen on the end of the bulb. 
The operation of the lamps was controlled by electronic switches in 
which an electron beam was rotated over a ring of 100 contacts. 

At the same time the old mechanical methods were pushed to the 
limit, and in June, 1932, Baird gave a demonstration of the Derby in 
a London theater using a three-channel transmission over a distance 
of 25 miles, each channel providing 10 lines of a 30-line picture 9X6 
feet in size. The projector consisted of a mirror drum with Kerr-cell 
modulation of the light. These events are mentioned because we 
must not forget the work of the old pioneers. By their spade work 
they were able to lay the foundations and excite the interest of the 
public, and thereby find the means whereby progress could be made 
and better methods developed. 
Early Color Demonstrations 

Before leaving the reference to these mechanical systems, we must 
mention the first large-screen color demonstration in Great Britain, 
which was presented by Baird as part of a variety program in the 
3000-seat Dominion Theater in 1938. Looking back at that demon- 
stration, in which a two-color process was employed in providing a 
120-line interlaced picture, we find that the results were remarkable, 
considering the state of the art at that time. 

Realizing then the limitations of the mechanical methods, we had 
before us two alternatives for providing a large-screen picture. First 
(Fig. 3) the intermediate film method which consists in photograph- 
ing the television picture reproduced on a small cathode-ray tube on 
to a film, which after rapid development, fixing, and drying can be 
projected as a standard film through the usual 35-mm projector. 
Second (Fig. 4) there was the cathode-ray-tube projection involving 
the stepping up of the faormal television receiver of the home to a 
higher power basis, so that intensely brilliant images of a size approxi- 
mately 6 inches in diameter can be projected by an efficient lens or 



1948 



THEATER TELEVISION IN ENGLAND 



133 




ACTUALITY PICK-UP. 



THEATRE PROJECTION. 



Fig. 3 Delayed large-screen projection by the intermediate film process. 
Television picture recorded on film at A. Film processed and dried at B. 
Film projected by normal projector at C. Delay, 5 minutes. 

mirror system to the full cinema screen size. This problem of the use 
of one or other of these methods, or of both of them, still exists today. 
First let us deal with the prewar studies of the intermediate film 
process, which was developed both in Britain and Germany, and dem- 
onstrated to theater audiences in 1935. This has the advantage 
that it is possible to provide the normal standard of brightness on the 
theater screen, because the processed film passes through a standard 
projector. The degree of definition achieved was reasonably good, 
but the method proved to be somewhat expensive, because of the high 
film costs incurred; and the attempt by our associated company, 
Fernseh A. G. in Berlin, to use a continuous loop of film, which was 
cleaned and resensitized in a continuous process in the intermediate 
film projector, was not attended with success. The 60-second delay 
in reproduction, due to the time of processing of the film, was not re- 
garded as a serious defect. Such equipment in practice, however, 
needed a very high degree of supervision, and the maintenance of the 




ACTUALITY PICK-UP. 



THEATRE PROJECTION. 

Fig. 4 Instantaneous electronic large-screen projection. 



134 



WEST 



August 



processing baths and of the mechanical parts of the projector was re- 
garded as being somewhat beyond the practical limitations imposed by 
the day-by-day continuous service of cinema projection. Neverthe- 
less, there were many who had, as many do now have, faith in this 
method of television presentation, because in addition to the possi- 
bilities of increased brightness and definition it has the additional ad- 
vantage that by putting the received television picture on film, a per- 



DEFLECTOR UNIT 




VISION AMPLIFIER 



TIME-BASE GENERATOR 



TALK-BACK AMPLIFIER 



TUBE ANODE 
CURRENT METER 



FOCUS CONTROL 



\ 



VISION CAIN 



Fig. 5 1938 Baird cathode-ray-tube projector for the 
10- X 7V2-foot screen in the Tatler Theater, London. 

manent record is made in the theater and this can be used over and 
over again in subsequent performances. 

However, further development of this process was dropped and 
efforts were concentrated on the cathode-ray-tube projection method, 
which appeared to offer the most scope for future practical develop- 
ment. It formed the basis of the equipment developed by the Baird 
Company for installation in 1938 and 1939 in the theaters of the 
Gaumont-British Picture Corporation. 

Theaters Equipped and Programs Provided 
Early in 1938, a small projector was installed in the Tatler 



1948 



THEATER TELEVISION IN ENGLAND 



135 



Newsreel Theater (Figs. 5 and 6). It housed a cathode-ray tube op- 
erating on 30,000 volts, and reproduced an intensely bright picture 
(3X4 inches in size) on the screen of the cathode-ray tube, which was 
projected by an //2.5 lens on to a screen 10 X 7 l /z feet. The illumi- 
nation on the theater screen was of the order of x /4 foot-candle, and the 
brightness, using a semireflecting screen material, of the order of l /% 
f oot-lambert ; and demonstrations were given of various actuality pro- 
grams transmitted on the 405-line basis by the B.B.C. These were 
mainly in the form of private demonstrations, and for a small theater 
of that type with a total seating accommodation for 650 people, the 
results were regarded as eminently satisfactory. The equipment was 




Fig. 6 Projection in the Tatler Theater, London, 
1938. 

entirely of an experimental nature and could not be handled by any- 
one but a specialist. 

These results gave encouragement for further work in larger thea- 
ters, and early in 1939 the Marble Arch Pavilion with a seating ac- 
commodation for 1290 persons was equipped with a higher power, dual 
cathode-ray-tube projector, using the pipe-shaped tube with metal- 
backed fluorescent screen, operating on 60,000 volts, with a Taylor- 
Hobson 12V 2 -inch//1.5 anastigmatic lens. (Figs. 7-10.) This pro- 
vided an illumination of l /z foot-candle on a screen 15 X 12 feet with 
a brightness of 1 foot-lambert in the high lights. This equipment was 
used for special programs on a commercial basis for paying audiences, 
and we well remember a red-letter day in large-screen projection in 
February, 1939, when a much publicized boxing match (the Boon- 






136 



WEST 



August 




Fig. 7 1939 Baird twin cathode-ray-tube projector at the 
Marble Arch Pavilion, London. 

Danahar fight) was reproduced to an excited and enthusiastic audi- 
ence who had paid up to two guineas (ten dollars at that time) for 
their seats in this theater for this particular event. The audience 
stood up and cheered on the conclusion of this fight, which fortunately 
went the full distance. Not a single person asked for his money 
back! The success of the results achieved led to the Gaumont- 
British Picture Corporation (whose President then was Mr. Isidor 




Fig. 8 1939 Baird twin cathode-ray-tube projector 
at the Marble Arch Pavilion, London. (Front view.) 



1948 



THEATER TELEVISION IN ENGLAND 



137 



Ostrer, a man of considerable vision, to whom we owe much for his 
encouragement of television in the early days), ordering twelve equip- 
ments for installation in the larger London theaters. By September, 
1939, the following theaters had been equipped with these projectors. 
Marble Arch Pavilion 1290 seats 
New Victoria Cinema 2564 seats 
Gaumont, Haymarket 1382 seats 
Gaumont, Lewisham 3047 seats 
Tatler Theater 650 seats 







Fig. 9 1939 Baird twin cathode-ray-tube pro- 
jector at the Marble Arch Pavilion, London. (Rear 
view of controls and cathode-ray tubes.) 

The incidence of war prevented the equipping of other theaters 
and thus the plan to have selected television programs presented at 
twelve London theaters to a total audience capacity of approximately 
22,000 was never realized. 



138 



WEST 



August 



At the same period Scophony, Limited, with its optical mechanical 
system with the supersonic light valve, equipped the Odeon Theater, 
Leicester Square, 2116 seats (Fig. 11), and certain news theaters, and 
were attracting full audiences for special programs. 

III. REQUIREMENTS FOR A THEATER SERVICE 

Before continuing with the historical development since the war, 
I would like to discuss briefly the requirements for a theater television 
service. 

The Complete Theater System 

It is the ultimate aim of the television engineer to provide the enter- 
tainment industry with a complete television system which can handle 



mr 




I 




Fig. 10 High-tension units at the Marble Arch Pavilion. 



and distribute all types of program material which will be of interest. 
The system and the equipment utilized therein can be conveniently 
divided as follows: 

(a) Pickup equipment consisting of cameras and associated equip- 
ment for synchronizing control for interior (such as studio and 
dramatic presentations) and for exterior (outdoor scenes) together 
with the necessary sound pickup, lighting, and power supply. 

(b) Film-scanning equipment. 

(c) Control-room equipment, for the purpose of selection and rout- 
ing of programs. 

(d) Distribution network, utilizing special cables or high-frequency 
radio channels. 

(e) Theater television projectors and loudspeakers. 



1948 



THEATER TELEVISION IN ENGLAND 



139 



Fig. 12 (a charter or ideal for British theater television engineers) 
indicates a possible system of pickup, control, distribution, and thea- 
ter reproduction which is capable of dealing with events taking place 
mainly in the London area, and of distribution not only to theaters in 
London but also in the provinces. At the same time it comprises 
provincial program sources also. 

Progress after the termination of the war has been concentrated 
under all the above head- 2 

ings, and will continue un- 
til there is evolved a satis- 
factory system which ex- JBlb^ 
hibitors will welcome as a 
valuable contribution to- 
ward their theater enter- 
tainment. The aim of the 
technician, who is primarily 
concerned with this aspect 
of television, will be to 
secure perfection independ- 
ently in each of the divi- 
sions of work enumerated 
above. 

Comparison with Film 
Projection 

The overriding problem 
is, of course, the develop- 
ment of theater television 
projection to a form cpm- 
parable to the present-day 
film projection. 

Such a program of work 
can conveniently be visual- 
ized in two stages: 

(1) The attainment of the utmost possible performance in each link 
of the 400- or 525-line system; alternatively the maximum possible 
to the 3-megacycle bandwidth limit. 

(2) The full equivalent to film projection (say 1000-line basis or 
20-megacycle bandwidth, or whatever it may be found to be). 




Fig. 11 Scophony supersonic light-valve] 
projector installed at the Odeon Theater, 
Leicester Square, London, 1939. 



140 



WEST 



August 



Satisfying the Exhibitor 

The exhibitor or promoter is our customer, and he presumably is 
capable of visualizing a true representation of what the public will 
require. It is our duty to satisfy him, if he wants it, by providing: 

(1) Instantaneous projection in theaters, from a given distribution 
center, of items of entertainment, of interesting events and actualities. 

(2) Delayed presentation from the distribution center. For ex- 
ample, daily films of local interest which are applicable to the theaters 
in a local area. 



LONDON Fi|m 
PROGRAMME Sfudios 
SOURCES [ 


West End Wemble 
Theatre:; Stadiun 
(Stage) (Footba 


y Lord's Harrinqay Alb< 
i Ground Arena Ha 
1 (Crcket) /Boxing) "ffuV 


rt Mobile 
L. ^ts 


Cable 

Cable 
Cable 1 


Cablef 
Cable 
Cable 


Wimbledon 
( Tennis 


V 


DISTRIBUTION 
CENTRE 
(LONDON) 

LON 
THE/ 


r " ' 

FILMS 


' > 1 STUDIO 1 | 


CO NT 


g| 
| 








Cable 

DON 
0-RES 

l\ 


Radio Pr 


Provincia 

ogrammeSources 




< ^ 







1 Radio I Links I 

PROVINCIAL THEATRES 

I I I 

Birmingham Manchester Glasgow etc. 

(D<2)<D (D@(D 

Fig. 12 Proposal for nation-wide theater television 
network. 

(3) Delayed presentation in individual theaters where the program 
planning is impracticable to admit of (1), or requires re-presentation 
additional to that given by (2). 

All these needs must be provided with the qualities of normal film 
projection. 

There may be, there are sure to be, other requirements as well, but 
for the moment we, as technicians, have many problems to solve (even 
in black-and-white only), and they will take time. However, I must 
emphasize that the theater owners and exhibitors must also spend this 






1948 THEATER TELEVISION IN ENGLAND 141 

period usefully in studying the possibilities and limitations of the ap- 
plication of television and in trying to decide how they. want to use it 
as a means of entertaining, attracting, and even educating the public. 
There is no doubt that we are up against this problem of what to do 
with television in the theaters, and we are entitled to ask, and to re- 
ceive, an answer to this question, while we are working on our purely 
technical problems, the solution of which is inevitable in the course 
of time. I should not, however, like to be too optimistic at this mo- 
ment by saying that we have ready a system which we can present 
immediately to the exhibitor in the form suggested earlier in the paper. 
It may be three years or it may be more before we can provide the 
brightness and definition in the quality of the picture which will be 
necessary, for the exhibitor to mingle his television with his film pro- 
gram; but it may be that he will find it profitable to consider an inter- 
mediate step whereby the television program can stand on its own 
merit without achieving the full technical results of the film projec- 
tion, and by segregating the television from the film program, or the 
television theater from the film theater, can give us an opportunity of 
gaining practical experience in the new technique. 

It may well be, on the other hand, that the new art will not be con- 
stricted to such applications, but will break out, with success, in an en- 
tirely new medium of application, which we have so far not visualized. 

I look forward to a more careful consideration of all the points by 
those who are responsible for the provision of public entertainment, 
and by such people who have the imagination and initiative to make 
practical use of the new tool which is now being forged. 

IV. POSTWAR DEVELOPMENT 

Progress Toward Setting up a Theater Service 

The keynote of the resumption of work on television in the 
autumn of 1945 was set by the British Government Television 
Committee, which issued a report in that year setting forth its deliber- 
ations regarding the reinstatement and development of the tele- 
vision service after the war, with special consideration given to (a) 
the extension of the service to the larger centers of population, (b) en- 
couragement of research and development, and (c) guidance to manu- 
facturers of equipment. 

Although 2*/2 years have elapsed, and very little has been done 
under (a), (b), or (c), I should say that the report was extremely good 
and showed that full consideration had been given by the Committee 



142 WEST August 

to the various aspects of television technical, commercial, and 
political. 

So far as it concerns us, I should like to quote a few sentences from 
the report. Thus, under the heading "Television in the Cinema," 
after stating that "The Committee had not been unmindful of the 
potentiality of cinemas for displaying television programs," the report 
went on to say: 

"Before the war certain firms were interesting themselves in the 
production of apparatus for this aspect of television, and a few cinemas 
had acquired equipment capable of projecting a picture of large size 
on the screen from a position in the stalls. Such apparatus was used 
with some success on occasions when events of outstanding public 
interest were televised." 

Then it goes on to say later : 

"We are encouraged to believe that the cinema industry and the 
British Broadcasting Corporation Working in co-operation and not as 
competitors in the exploitation of television, will achieve consider- 
able results of a character beneficial to both." 

And further : 

"Although television in the home would compete with the cinema 
for the public's interest, the extension side by side of the two forms of 
entertainment should on the whole prove mutually helpful rather 
than otherwise, and home and cinema television are likely to have a 
stimulating effect on each other." 

And, finally: 

"We recommend that close attention should be given to the possi- 
bilities of the use of television by cinemas." 

This report was accepted by the British Government and issued in 
the form of a white paper, but since that date no official pronounce- 
ment has been given indicating that these recommendations have been 
implemented in any way, or that any steps have been taken to give 
effect to them or to encourage the cinema industry in its work on these 
problems. I shall deal further with this point later on, but for the 
moment I should prefer to submit to you details of the work which 
has been done by commercial companies, and in particular by my own 
Company with the encouragement of Mr. J. Arthur Rank, and of the 
results achieved in the two years since we started thinking about tele- 
vision again in the autumn of 1945. During this period, we have 
seen the development and application of many new types of equip- 
ment which have an important bearing on our work ; for example, new 



1948 THEATER TELEVISION IN ENGLAND 143 

types of television cameras, of scanners for film and still pictures, new 
means of distribution by radio or by cable, and theater projectors 
either of the cathode-ray-tube type with lens and mirror systems or of 
the intermediate film type, or of the storage type. 

Comparison with Cinema Standards 

Before considering these in detail, let us consider five main head- 
ings (which possibly can be regarded as separate factors, but which in 
practice are all interlinked), to provide a basis of comparison with the 
accepted standards of the cinema. 

(1) Picture definition, or detail of the reproduced picture. 

(2) Picture quality or faithful reproduction of the tone values, from 
black through the half tones to white. 

(3) Brightness of the reproduced picture, and its color. 

(4) Freedom from interference, flicker, spurious patterns and effects, 
shading, and background noises. 

(5) Cost of manufacture of the equipment and of its installation and 
maintenance. 

Performance of Equipment 

Let us now make a brief review of the various types of equipment 
already developed on both sides of the Atlantic, demonstrated in Eng- 
land, and also able to be manufactured. 

(a) Cameras. You are quite familiar with the operation and char- 
acteristics of the various types of television cameras, so I need not go 
into them in detail, except to say that with the iconoscope we acknowl- 
edge its superiority in definition, but also its limitation in the produc- 
tion of undesired shading effects which cannot be controlled. The 
image iconoscope has the advantage of a little more sensitivity than 
the iconoscope and less shading troubles. The orthicon with its even 
field of picture rendering is free from shading, but loses detail; and 
the image orthicon with its enormously increased sensitivity, suffers, 
however, from background noise and great difficulties in manufacture. 

(b) Film Scanners. There are those, like the Mechau continuous- 
motion mechanism, installed at the B.B.C., which use the iconoscope, 
and therefore also suffer from shading distortions of the picture grada- 
tion. There is the Farns worth dissector film scanner which gives an 
even field, but is difficult to set up to avoid geometrical distortion of 
the picture. And finally, there is the cathode-ray-tube flying-spot 
scanner, which can give, under controlled conditions, as good a 



144 



WEST 



August 



picture as you would wish to see, with excellent definition and quality, 
and free from shading. 

(c) Caption or Still-Picture Scanners. The same remarks apply. 

(d) Means of Distribution. By radio links, which can carry the full 
requirement of frequency range, which are flexible in setting up and 
operation, but which may be subject to interference. 

By cable, with limited frequency band and high capital cost. 





Fig. 13 Lens and mirror electronic projectors. 

MIRROR ARCLICHT PROJE< 

f 



OPENING 6 CLOSING 
OF APERTURES IN SCREEN 
CONTROLLED BY CATHODE 
RAY SCANNING BEAM. 




LARGE 
SCREEN 



FOCUSING SYSTEM 
CATHODE CUN 

Fig. 14 Electronic storage projection system. 

(e) Projection. Cathode-ray-tube projectors, either using a wide- 
aperture anastigmatic lens or a Schmidt-mirror system, with its great 
advantage. (Incidentally, I remember testing a Schmidt projection 
system in 1937.) (Fig-. 13.) 

Intermediate film projectors, in the operation of which much ex- 
perience still is to be gained. 

Storage projectors (described in principle in Fig. 14) of which only 
one type so far has been shown to be reasonably practicable, namely 
the AFIF system developed by Professor Fischer of Zurich. (Figs. 15 
and 16.) 



1948 



THEATER TELEVISION IN ENGLAND 



145 



(/) Screens. Types of screens with higher reflection coefficients 
than the normal matte white screen, such as the established types of 
beaded or silver screens; new types of screens coated with material 
which is a combination of matte white and silver; and lenticular types 
of screens varying from the crudely stippled metal screens to the opti- 
cally designed lenticular screens which project all the received light 
back into the audience seating only. (Figs. 17 and 18.) A screen 




Fig. 15 AFIF storage large-screen projector. 

having a reflecting cone with a vertical angle of .40 degrees and a total 
horizontal angle of 104 degrees would be ideal for the average theater. 
(Figs. 19 and 20.) 

Arising out of the consideration of the qualities of the various types 
of equipment referred to (lack of time prevents me from going into-a 
detailed study), we have in my Company evolved an experimental 
405-line system which has already been the subject of practical tests, 
and which for the present consists of : 



146 



WEST 



August 



Telecameras 

The image orthicon or image iconoscope. 
Telecine 

Cathode-ray-tube flying-spot film scanner. (Fig. 21.) 
Telecaption 

Cathode-ray-tube flying-spot still-picture scanner. (Figs. 22, 23, and 24.) 
Teledistribution 

Radio links operating with a few watts on a frequency of 480 megacycles at 
distances up to 12 miles. 

Teleprojectors 

' A Schmidt mirror projector (Figs. 
25 and 26) having a 27-inch di- 
ameter mirror, and an 18-inch di- 
ameter plastic correcting plate; 
with an aluminum-backed straight- 
through cathode-ray tube, operat- 
ing on an anode voltage of 50,000; ! 
mounted in the stalls, or on the 
front of the balcony; remotely con- 
trolled from a console installed at 
the back of the stalls or in the pro- 
jection box. (Fig. 27.) 
Theater Screens 

Of a type where the reflected 
light is concentrated into the area 
occupied by the audiences. 

I must now state the prac- 
tical results achieved in terms 
of the fundamental points of 
performance which I have 
specified above. 

(1) The definition over the 
whole system is such that 3- 
megacycle vertical bars are re- 
solved in the picture without 
any noticeable phase defects. 

(2) The measured high-light 
brightness on a 14- X 11-foot 
stippled metal screen in the 
direction normal to the screen 
down the center line of the 

theater, is 5 foot-lamberts, compared with the accepted film stand- 
ard of 7 to 14 foot-lamberts, and the measured black brightness j 
is 0.1 foot-lambert; the average contrast range during a succession of 
pictures is 30:1. At 30 degrees off the center line the high-light 
brightness is 2.5 foot-lamberts. The output of light from the projec- 
tor with no picture, and running at a brightness corresponding to the 
maximum usable high-light brightness for a good quality picture i: 




Fig. 16 AFIF storage projector. 

16, 17 Arc lamp. 

1 Eidophore oil film scanned in 
vacuum by the cathode-ray beam 8. 

4,5 Heat-absorbing bars. 

19, 20 Lens and mirror projecting 
the picture on to the screen 21. 



1948 



THEATER TELEVISION IN ENGLAND 



147 



300 lumens. A new projector, almost completed, will provide a light 
output of 600 lumens, adjusted for conditions for good quality picture 
projection. By the time we get into the London theaters we hope to 
project 1000 lumens on to the screen. The color of the picture is off- 
white in the direction of cream. Fig. 28 indicates the progress of 
definition and brightness over the years, in comparison with the de- 
sirable results which are equivalent to the average characteristics of 
film projection in theaters. The important point about these curves 
is that the upward tendency continues and there is no sign yet of a 
slowing up of progress, which might be indicated by a flattening of 
the curves. 



VMWT WHITE 




CBVSTAL BEADED 



Fig. 17 Polar diagrams showing reflectivity 
of types of screens at various angles with the 
normal to the screen, compared with that of the 
matte white screen which is represented by the 
circle of radius 1. 



(3) The estimated over-all quality curve is approximately linear over 
the range from black to two thirds the high-light brightness specified 
in (2) above, and flattens out above that figure. For example, we 
have measurements indicating a brightness curve for the projector as 
follows : 

A gamma of l /z in the shadows, caused mainly by scattered light. 

A gamma of 2 over the greater part of the curve up to 2 / 3 high-light 
brightness. 

A gamma dropping to 1 / 2 at the upper values of brightness due to 
electron-beam defocusing at high current, saturation in the fluorescent 
powder, and other causes. 

This distortion, if measured correctly, can be mostly made good to 
provide an over-all constant-gamma condition. 

(4) With regard to freedom from interference, I must admit that there 



148 



WEST 



August 



is much to be desired with existing standards, and with relatively un- 
controlled local noises. Under the best conditions these can be a rela- 
tively unimportant factor, but on occasions the interference may be 
troublesome and cause annoyance to the spectator. 

Proposals for an Experimental System for the London Area 

The complete system described above, and which is in practical 
operation in an experimental form, and can be engineered in a form 
suitable for the production of a serviceable instrument, is, in my 




i A ; 5-!O 
I 2 ' 5 

H undf O-S 




Fig. 18 Pictorial representation of screen-brightness 
distribution in a theater for various types of screen, subject 
to a given value of illumination. 

opinion, a first practical solution which we can offer to the cinema in- 
terests. It is a long way ahead of the 1939 equipment. It is up to 
them to decide how, where, and when they can use it to advantage. 

Our recommendation is to set up a sample system in daily operation 
for invited and paying audiences. Fig. 29 illustrates a plan of a pro- 
posed experimental system which we hope to work put during 1948 to 



1948 



THEATER TELEVISION IN ENGLAND 



149 



give us this experience. You will see that programs are to be pro- 
vided from three centers, the B.B.C. Studios at Alexandra Palace in 
the north of London, the Pinewood Film Production Studios of the 
Rank Organization to the west of London, and the Crystal Palace site 




PROJECTOR 



CINEMA SCREEN^ 



ELEVATION OF CINEMA 



Fig. 19 Elevation of average theater showing the angle 
required for screen reflection in the vertical plane. 




Fig. 20 Plan of average theater showing the angle required for 
screen reflection in the horizontal plane. 

on the southern side overlooking London, where we shall set up a cen- 
tral receiving station and retransmitting station, and some local 
scanners for the transmission of films, interviews, and announcements. 
The radio links will be on frequencies just above and below 480 mega- 
cycles. Retransmissions will be beamed, from the Crystal Palace, 
with an angle of 10 degrees in the direction of certain theaters which 



150 



WEST 



August 



are suitable for the install ation of the pro j ec tion equipment . We have 
in mind four West End theaters and two suburban theaters. One 
beam will suffice to cover the London West End cinemas and a se- 
lected northwestern suburban cinema, and another beam will cover a 
suburban cinema in the southeastern area of London. 




Fig. 21 "Cintel" flying-spot (35-mm) film 
scanner. (Scanning tube in left-hand box, optical 
system and gate in center, multiplier phototube in 
right-hand box.) 

Figs. 30 and 31 are elevations of two of the selected cinemas show- 
ing our proposals for equipping them. 

Audience Reaction 

So far, nothing has yet been done, so far as I know, on either side 
of the Atlantic, which would give the exhibitor some practical figures 



1948 



THEATER TELEVISION IN ENGLAND 



151 



and experience to gauge future public requirements. We badly need 
experience on public reactions to a regular service beyond the stage 
when television was just a novelty and used only on special occasions. 
We recently invited a cross section of our employees to see a pro- 
jected B.B.C. program (lasting l -1 / 4 hours) in the cinema which we had 
equipped with the projection installation described above. These 




Fig. 22 "Cintel" flying-spot caption scanner. (Scan- 
ning tube below, lens and phototube box in center, 
monitor tube above.) 

employees had been working some distance away in other factories, 
and had not seen any large-screen pictures before. The entertain- 
ment value of the program projected happened to be poor. This was 
beyond our control, but we were surprised at the tone of the response 
to the questionnaire which was circulated to each employee after- 
wards, asking for impressions. The total number concerned was 264 
and there was a good mixture of technical, clerical, and administrative 



152 



WEST 



August 




Fig. 23 Still picture transmitted on 405-line basis by "Cintel" 
caption scanner. 

(nontechnical) staff, bench workers, wiring and assembly girls, and 
glass workers, and the following is the analysis of the voting papers : 




Fig. 24 Still picture transmitted on 405-line basis by "Chite!" 
caption scanner. 



1948 THEATER TELEVISION IN ENGLAND 153 

AUDIENCE REACTION FIGURES 

1. The picture was generally: better than expected 129 

as expected 83 

not so good as expected 52 

total 264 

2. The picture was : adequately bright 165 

not bright enough 99 

total 264 

3. The detail was: just sufficient 79 

not quite enough 145 

not nearly enough 35 

nonvoters 5 

total 264 

4. The picture caused: some eyestrain 158 

no eyestrain 101 

nonvoters 5 

total 264 

5. The picture: is good enough 163 

is not good enough 96 

nonvoters 5 

total 264 

,o justify reproduction on large screens of certain events of general interest, i.e., 
he Boat Race, Test Cricket, football, etc., to paying audiences. 

So much for what might be termed an average audience. 

Now to come to an audience of enthusiasts, where there is no ques- 
ion at all regarding the practicability of utilizing large-screen tele- 
dsion up to its present degree of performance. 

We were invited at the beginning of the month to assist at the Con- 
servative Conference which was held at Brighton on the south coast of 
England, in the large 3000-seater Dome, built in the oriental style, by 

ing George IV in 1805. As an attendance of 4000 persons at the 
Conference was anticipated, room had to be found for an overflow 
neeting in the Dolphin Theater, a 1000-seater, and about 500 feet 
iway from the Dome. We set up image-orthicon cameras, manufac- 
,ured for us by the Du Mont Company, facing the platform in the 
Dome, one for the close-up of the speakers and the other for a general 
/iew of Mr. Churchill's Shadow Cabinet on the platform. The picture 
vas reproduced on a 14- X 11-foot screen on the stage of the distant 
heater, on a 405-line basis, with a Schmidt projector operating on 



154 



WEST 



August 



40,000 volts, and giving a high-light brightness down the center of 
the theater of 4 foot-lamberts. To enable the delegates to study their 
agenda papers there was about */* lighting left on in the theater. We 
had accepted this invitation to gain experience, and we certainly did 
get that experience from the enthusiastic Party representatives, espe- 
cially on the occasion when their Leader was speaking. Throughout 
the three days of the Conference, the theater was filled to overflow- 





1 



Fig. 25 "Cintel" mirror projector 
for 16- X 12-foot screen. (Front 
view.) 



Fig. 26 "Cintel" mirror projector 
for 16- X 12-foot screen. (Rear 
view.) 



ing, and many of the visitors preferred the close-up of the speakers on 
the large screen to the more distant view in the large Dome. On 
the last day, I sat at various points in the theater and took Leica 
snapshots, at exposures of l / w of a second, using an f/2 lens and Super 
XX film, of the large-screen results, and I am happy to be able to pre- 
sent some of the results here, ahd I am more than happy that they 
represent one who is, I believe, regarded throughout the world, anc 
even in Britain also, as one of the greatest leaders of our time. (Figs 
32 and 33.) 



1948 



THEATER TELEVISION IN ENGLAND 



155 



Installation and Regulations 

Finally, there is one factor not to be ignored ; the installation prob- 
lem, especially in relation to national or local regulations which, when 
originally framed, did not envisage the use of television in theaters. 







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156 



WEST 



August 



In Great Britain the authorities are busy drafting more and more 
new regulations. Everything has to be regulated. The old original 
Cinematograph Act of 1909 (amended only once since that date in 
1923 and before the advent of sound, and still legally in force) would 
close half the cinemas in the country if the letter of the law were ob- 
served. A new amendment of the old Act is now in preparation, and 
has been drafted, and would, according to the exhibitors, close all 
cinemas. Clauses have been drafted in anticipation of the installa- 
tion of television equipment, and in such a form (I should say without 
malice aforethought) that would make it quite impossible to install 



FOOT 

LAMBERTS 



NUMBEP 
OF LINES 



AVEPAGE CINEMA PROJECTION 



800 

600 
500 

4OO 

250 



CINEMA PROJECTION EQUIVALENT 



1938 1939 1946 1947 1948 1949 S5O 



1938 1939 1946 1947 1948 1949 I9SO 



Fig. 28 Progress of brightness and equivalent definition in large-screen 
(16- X 12-foot) television projection. 



television in cinemas. For example, the draft stipulates that a tele 
vision projector set up in the theater must be completely surrounde 
by 14-inch brick walls without any doors. We have visions of th 
projectionist being built in with the projector and remaining there a 
the rest of his life. But I must admit that the authorities are, how 
ever, open to suggestions for improvements in the regulations. 

In actual practice, we have never had any difficulty in satisfyin 
local authorities from the points of view of safety and fire. We hav 
found them most co-operative and as anxious to gain experience ir 
the new type of equipment and its installation as we are. 



1948 



THEATER TELEVISION IN ENGLAND 



157 



V. PRESENT PROBLEMS " 
(REQUIREMENTS FOR THE IMMEDIATE FUTURE) 
I have dealt with the present state of the art in Great Britain. I 
may have painted, perhaps, too rosy a picture, but I prefer to be an 
optimist, recognizing that we still have a long way to go. Our present 
problems are as follows : 

(1) Technical 

We have to improve detail, quality, projection brightness, and free- 
dom from miscellaneous minor but irritating defects. I prefer to 



PALACE 
ision Studios 




STUDIO 
(Telecameras)(Telecin<)(Contiol> 



Fig. 29 Proposed experimental cinema-television-distribution plan 
in the London area. (For 1948.) 

group all these points together and to refer to some of the funda- 
mental problems associated with all of them. 

(a) Number of Lines for Theater Standardization. We have seen 
many references to the 1000-line desirability. On the other hand, we 
have often heard that our 405-line system at its best is enough. That, 
of course, refers to a controlled local picture. Therefore, ignoring for 
the moment all the excellent work which so far has been done in try- 
ing to establish the minimum basis for either home or large-screen pro- 
jection, we decided to start afresh and^make a practical investigation 
with many observers, of the brightness-resolution contrast relation- 
ship in projected pictures. 



158 



WEST 



August 



Some of the preliminary conclusions are given in Fig. 34 which show 
the result of observations made on line patterns of various dimensions 
exhibiting varying degrees of contrast and illuminated at various 
values of brightness. The curves in the diagram connecting bright- 
ness resolution and contrast should be taken as indicative of the order 
of magnitude involved where the unit of relative brightness represents 
the normal high-light brightness of a projected picture, say approxi- 
mately 10 foot-lamberts. The number N of test lines per picture 
height is equivalent to the number KN of lines of television scanning, 
where the factor K lies between 2 and 3. Curve A indicates that the 




HIGH TENSION UNI 



Fig. 30 New Victoria Theater, London. Proposed television 
installation with the projector in the orchestra stalls. 

eye can appreciate up to something between a 950- and 1400-line pic- 
ture at a brightness of 10 foot-lamberts; but in practice, according to 
curve D, the result of observations of projected films, it is satisfied with 
something between a 650- and 950-line picture at that brightness. 
Arising from this, it appears to be desirable that we should aim at a 
standard of something round about 900 lines for theater television, and 
up to 1200 lines, if we wish to record a picture on film which will pro- 
vide prints equivalent to normal film practice. 

(6) Systems of Scanning. We have got too much into the way of a 
tacit acceptance of double interlacing, based on a theoretical calcu- 
lation of its advantages. I am not at all sure that practice has proved 
this. 

At the recent Cannes Conference it was generally agreed that the 



1948 



THEATER TELEVISION IN ENGLAND 



159 



time was ripe for a renewed investigation of sequential processes. In 
fact, all the authorities there admitted, as a result of their practical 
experience of results using interlaced scanning, that they would prefer 
a 500-line sequential picture at 50 frames per second to a 1000-line 
interlaced picture at 50 frames, 25 pictures a second. 

The following defects are observed in interlaced scanning: line 
crawling, interline flicker, spurious pattern flicker, line breakup on 
movement, pairing or loss of interlace, unequal field brightness, ir- 
regularities and irritating effects on vision, and complexity of circuits 
and equipment. 




PROJECTOR 

REMOTELY CONTROLLED 

-.FROM CONSOLE 



HIGH TENSION UNIT 



Fig. 31 Gaumont Theater, Hay market, London. 
Proposed television installation with the projector on 
the front of the balcony. 



Some of these also appear with sequential scanning, with the added 
disadvantage for a given channel bandwidth of greater "lininess" and 
lower definition. 

The list of interlacing defects is formidable, and indicates the reason 
for disquiet as to the future of interlacing in improved television sys- 
tems. The advantages, however, such as terms of improved defi- 
nition, are not to be lightly disregarded. The final choice, to interlace 
or not, cannot be decided without further observational data. 

A number of various comparisons can be made, but they all resolve 
themselves into a choice between either a loss of definition or the pres- 
ence of flicker and stroboscopic defects. Other factors which will 



160 



WEST 



August 




Fig. 32 Mr. Churchill speaking by large-screen 
projection (14 X 11 feet). 

require attention in this investigation are the compromise between 
vertical and horizontal resolution, and the value of artificial means for 
line broadening to reduce "lininess." 

In drawing your attention again to sequential scanning, I should like 
to mention that recently we made an equipment to demonstrate the 




Fig. 33 Mr. Churchill speaking by large-screen 
projection (14 X U feet). 



1948 



THEATER TELEVISION IN ENGLAND 



161 



principles of scanning a picture and reconstituting it, for the Science 
Museum in London, in connection with the Electron Jubilee Exhibi- 
tion. We employed a scanning of 100 lines sequential, and the repro- 
duced picture had a remarkable element of stability; in fact the rigid- 
ity of a lantern slide, and we were not unduly bothered by the limita- 
tions of definition due to the low number of scanning lines. In my 
opinion, in introducing interlaced scanning we have deliberately tried 



500 



NUMBER 

OF 

TEST 

UNES 

PtR 

PICTURE 

HEIGHT 



300 



A. LIMIT OF VISUAL ACUITY * (MEAN 7 OBSERVERS) 

B. 35 M.M STANDARD RELEASE PRINT (tow POWER MAGNIFICATION) 

C. AS B, SINGLE FRAME STILL PROJECTION VIEWED ON SCREEN 

AS C, BUT STANDARD VICWIN6 DISTANCE * 
# VIEWING DISTANCE 4-X PICTURE HEISHT 







RELATIVE BRIGHTNESS 

Fig. 34 Investigation of brightness-resolution contrast characteristics. 
Data for center of field, with low-contrast test object. (Density difference 
0.3, equal line width line spacing.) Constant "average" brightness of picture. 

to deceive the eye, and the eye will not stand to be deceived, and it is 
in this connection that we shall find advantages when we come to 
achieve any system of storage projection. 

We have made some interesting tests, originally out of curiosity 
more than anything else, to compare the results of projecting, one after 
the other, an intermediate film picture and an interlaced electronic 
picture on the large screen, of the same subject scanned with the same 
number of lines, and we were remarkably surprised at the amount of 
irritation, as you might describe it, produced by the interlaced pro- 
jected television picture on the eye, in comparison with the steady 



162 WEST August 

restfulness of the projected intermediate film picture. I have an idea 
that here we have a vital point regarding vision which needs much 
more study; and, furthermore, that an electronic sequential picture 
will occupy an intermediate place between the other two regarding 
the general stability and freedom from irritation (and from consequent 
headaches) desirable for large-screen projection. 

(c) Channel Bandwidth. We have had to change our minds during 
the last two years regarding the amount of intelligence which can be 
carried on a 3-megacycle channel. Now we find that we are able to 
squeeze much more apparent detail and quality into a channel with a 
definite cutoff at 3 megacycles, and we have been remarkably sur- 
prised at the general increase of performance which has been achieved 
by correcting for response, phase, gamma, and other requirements 
throughout the whole system within this limitation of frequency. Up 
to now for the 1000-line transmission, the bandwidth of up to 20 mega- 
cycles has been mentioned. We believe that we shall achieve all we 
want to do by concentrating on obtaining the maximum value that 
can be obtained on a channel up to 12 megacycles only. 

(d) Quality of Picture. We have been in the past, I feel, content tc 
have seen occasionally, when all conditions were right, a picture oi 
good quality, and then to feel that we had achieved a result which 
would be universally acceptable. It is only recently that a full study 
has been made of the component and over-all linearity of the system 
and that steps have been taken to correct errors in gamma. This 
process of gamma control, which ensures that the relative brightness 
of parts of the reproduced picture bear a linear relationship to the cor- 
responding parts of the picture being scanned, is of vital importance 
in ensuring a picture of first-class quality. It is only when a system 
has been set up which complies reasonably well with this condition and 
registers an over-all gamma of about 1 that one realizes the enormous 
improvement in general quality of the picture. As regards projection, 
I am convinced that so far no projector of any type complies with this 
condition. As previously mentioned, there is a distortion of the 
gamma curve, particularly in the high-light region, and this must be 
corrected, first, by studying each element of the system in turn, and 3 
second, by applying -an over-all correction when each element has 
been improved as far as it will go. 

(e) Picture Brightness. In the cathode-ray-tube projector the curve! 
connecting brightness with anode voltage on the cathode-ray tube ; 
and the curve connecting brightness with beam current, both 



1948 THEATER TELEVISION IN ENGLAND 163 

saturation, which begins at a certain high-light brightness on the 
viewing screen. The problem of extending the brightness curves is 
one of the most important that we have at the moment. This in- 
volves the following studies: 

(i) The development of optical systems of the mirror type to even 
greater efficiency than the Schmidt. 

(ii) The development of tube electronic characteristics so that de- 
focusing is controlled with an increase of voltage and current. 

(iii) The development of a fluorescent material and its application 
to the face of the tube, studying in particular the problems of high- 
current saturation, defocusing, and halation in the layer; and also its 
color and life characteristics. 

(iv) The development of the viewing screen providing more econom- 
ical use of the light projected on it, so that it is reflected back where 
it is required and not dissipated throughout the theater. 

(2) Distribution Systems 

Considerable study has been made of the relative advantages and 
disadvantages of cable and radio means of distribution. On behalf 
of the radio link, we find lower capital and running costs, more flexi- 
bility in operation, and against it the scarcity of channels, and inter- 
ference ; on behalf of cable, a clear and undisturbed channel (at 
least we hope so), and secrecy; against cable, the high cost of in- 
stallation, resulting in high rental charges, and the length of time be- 
fore the installation can be carried out, due to higher priority for in- 
stallation labor. In Great Britain, both radio and cable links are 
controlled by the Postmaster General, and in the setup of a radio sys- 
tem of a permanent nature, such a system would most likely not be 
licensed for commercial operation, but would be taken over by the 
Post Office to operate in whatever manner it thinks fit. However, the 
exceedingly high charges for the rental of coaxial cables (something in 
the nature of 600 per mile per annum for a 3-megacycle cable has 
been quoted) with no definite date of availability promised within the 
next five or ten years, makes it imperative to provide experimentally a 
radio-link system, and the first steps in this direction already have 
been described. In the meantime, the first link in the provincial dis- 
tribution system of B.B.C. television programs has been started. 
Work has commenced on a radio link between London and Birming- 
ham to operate on 900 megacycles. 

Although you are, for your own commercial cinema schemes, 



164 WEST August 

pressing for allocations of frequencies above 1000 megacycles for radio 
links, we are pressing for the 500- to 1000-megacycle band, because this 
range offers, in our opinion, advantages for wide-band television which 
may not be possible in the regions above 1000 megacycles. 

(8) Program 

Here we have many problems, the majority of which are outside 
our technical province. I have already referred to some of them. 
Others causing us much thought in England are as follows : 

(a) License to Operate Commercially. Over two years ago we asked 
the government to consider giving us facilities to operate on a com- 
mercial basis between our studios and theaters. The permission 
is concerned with the means of transmission and distribution. In 
other words, we ask for a license to use the ether or the facilities pro- 
vided by Post Office cables. In this respect we are dependent on the 
Television Advisory Committee (which has taken the place of the 
original Television Committee), and this Advisory Committee has 
been taking plenty of evidence during the last two years but has been 
very slow in making the appropriate recommendations to the Post- 
master General who would present them, if he agreed, to Parliament 
for latification. 

(b) Three-Cornered Interests. It may be that although the report 
of the Television Committee advised that steps should be taken to- 
ward the encouragement and establishment of a television service for 
cinemas, the delay in the granting of a license to operate commercially 
has been mainly due to the difficulty of getting together in agreement 
the three interests who are mostly concerned : 

(i) The B.B.C. and its home viewing audience. 

(ii) The promoters of sporting events, some of which can be classi- 
fied as being of a national nature. 

(iii) The cinema interests. 

Therefore, if these three could be got to work together in harmony, 
with full co-operation in the provision and exchange of program ma- 
terial, the authorization of a license which would give the cinema in- 
terests a start in commercializing television might be forthcoming. 
However, pressure in this direction is bound to come when technical 
results are obtained, which justify in themselves that a perfected in- 
vention of this nature should be utilized for the nation's benefit. In 
any case, as the price of home television receiving sets is for the time 
being higher than the purchase level of the majority of the population, 



iy4o 



THEATER TELEVISION IN ENGLAND 165 



is not television in the cinema the average man's way of participating 
in this form of entertainment? 

(c) Place of Television in the Theater Program. What do theater 
interests intend to do with television? This is a question which, as 
mentioned before, needs very careful study of all factors by the enter- 
tainment industry. I have not yet heard a balanced and well- 
thought-,out reply to this problem. 

Are we wrong in assuming that large-screen television and cinemat- 
ographic projection can be made complementary to each other? 

Can we show them both in the same program? 

On the long or very long view, the answer is yes. 

But in the meantime, those who have financed its development must 
be thinking of some return. In which case, can we commercialize on 
an intermediate stage either by (i) provision of specialized television 
theaters; or (ii) provision of television in cinema theaters, but tele- 
vision and film each taking a separate and independent program 
period for itself. 

(d) Instantaneous Versus Delayed Action. I am not at all clear as 
to the relative uses of instantaneous electronic projection of television 
in theaters, and the delayed-action presentation by using the inter- 
mediate film process. There are so many factors controlling the tim- 
ing of programs in theaters that it would be extremely difficult to 
guarantee that all theaters taking a particular program would be 
standing by at exactly the correct moment. On the other hand, I 
cannot visualize the practical operation and maintenance of inter- 
mediate film equipment in individual theaters. 

There is one thing of which I am quite certain. I have many times 
experienced the tenseness of an audience watching, as it is taking 
place, on the cinema screen, a national event, the outcome of which is 
unknown, and I am convinced of the enormous entertainment value 
of such an item. The satisfaction which I personally have experi- 
enced ori such an occasion has been acknowledged also by all those 
present. The important point is that the event is being watched as it 
is happening, and half the entertainment value would be lost with 
delayed presentation. 

I feel, however, that the best way out of this problem is not by writ- 
ing and talking, but by setting out to obtain practical experience in 
both methods over a period of time; such work to be done in close co- 
operation between the technicians and the leaders of the entertainment 
industry, and it is only by facing this problem fairly and squarely that 



166 WEST August 

we can really get a solution that will satisfy future requirements in 
the provision and extension of the cinema television service. 

(4) General Economic Problem 

Although I am not qualified to discuss this subject, I feel that this 
is a matter which must not be left unmentioned in a general survey of 
this nature. 

In looking ahead, as the technician must look ahead, toward the 
future of the entertainment industry and the impact of technical 
progress on it, we must attempt to visualize the various possibilities 
which may arise, so that we can provide information for those whose 
duty it is to study the economic trend in relation to the ever-changing 
needs and tastes of the public served by the industry. Here we have 
in large-screen television a new tool rapidly approaching the practical 
stage where it can be of value for entertainment and education. It 
is our duty to give guidance, as far as we can, so that it can be used to 
the best public advantage. I hope that this paper will, in describing 
past experiences, and in discussing present problems and future possi- 
bilities, make some contribution in this direction. 

VI. CONCLUSION 

Finally, I should like to put to you a few questions, based on my 
remarks, and eagerly await your considered replies : 

(1) Do you agree that the presentation of large-screen television to 
the public should be made in two distinct stages? 

Stage (i) on the 400- or 525-line basis, or the 3-megacycle band- 
width limit. 

Stage (ii) the equivalent to film projection. Or should we wait until 
Stage (ii) is an accomplished fact? 

(2) What do you regard as technical requirements for Stage (ii)? 

(a) Number of lines. 

(b) Sequential or interlaced. 

(c) Bandwidth. 

(3) Should we really make a comparison with film projec- 
tion? Should not public television develop as a different medium, 
and to a different standard? 

(4) What will be the comparative practical uses for : 

(a) Film intermediary. 

(b) Instantaneous electronic projection. 

(5) How will theater television be used by the entertainment 
interests? 



1948 



THEATER TELEVISION IN ENGLAND 



167 



ACKNOWLEDGMENTS 

I must give credit and appreciation to the members of my team, who 
work with unequalled enthusiasm and unity of purpose in endeavor- 
ing to solve our problems: Messrs. T. M. C. Lance, J. D. Percy, T. C. 
Nuttall, L. C. Jesty, L. R. Johnson, K. A. R. Samson, E. McConnell, 
M. Morgan, J. E. B. Jacob, and many others; also to Dr. C. Szegho, 
now with the Rauland Corporation; and to Dr. Starkie of Imperial 
Chemical Industries (Plastics Division) who has carried out the opti- 
cal work for projection; and Mr. Warmisham of Taylor Hobson for 
the optical work on the scanning side. 

NOTE : Following the delivery of his paper, Mr. West showed a 
short film, divided into two parts: (1) the recording of B.B.C. pro- 
grams with particular reference to faults encountered, and (2) the 
recording of pictures transmitted by "Cintel" film and caption 
scanners. 

DISCUSSION 

MR. FRASER: Was the film that was just shown a 16-mm film? 

MR. A. G. D. WEST: Yes, reversal 16-mm film. 

MR. ERASER: Has anyone attempted to count the number of scanning lines to 
see if there are 405 or 202 Va? 

MR. WEST: I think it is likely that there is quite a lot of pairing. As I have 
mentioned, we are concerned about the difficulties of correct interlacing. We have 
an idea that not more than 10 per cent of receivers interlace properly. Does that 
hold on this side of the Atlantic? 

MR. SIEGFRIED: What is the greatest projection distance that Mr. West has 
employed with practical results, and what is the largest picture? 

MR. WEST: The projection distance maximum is 40 feet from the screen. We 
have not been farther back than that. 

MR. BEN SCHLANGER: There was one of the theater diagrams which you showed 
which had a television projector on the face of the balcony. It did seem to me as 
though that was one of the best locations. The projector did not seem to obstruct 
the view from any part of the audience. It seems to be the most practical job. Is 
that true? 

' MR. WEST: Yes. We fully agree with that. We should be very pleased to see 
theaters which had balconies coming out to, say, 50 feet from the screen. That 
would be the ideal position for the projector, but few existing theaters satisfy that 
condition. Most of them are 70 or perhaps 90 feet back. 

MR. SCHLANGER: In contemplation of building a new theater, might that be 
the course to follow? 

MR. WEST: Yes, sir. Obviously it would be preferable to have the projector 
back in the box which is the right place for it, but in determining the best position 
for the projector in the auditorium we are subservient to the economic cost. I be- 
lieve that we could produce a large projector with a 40-inch mirror which could 



168 WEST 

be put in the projection box, and would provide sufficient brightness, but it would 
be very expensive. The glasswork alone might cost about $16,000 and further- 
more the production output would be very slow. I believe it is the same over here. 
It might take two years to produce one only. It, therefore, appears to be neither 
an economic nor a practical proposition. 

We, therefore, have to compromise with a smaller mirror, smaller dimensions of 
projector, and a smaller throw distance to secure the brightness for a given size 
screen. If theaters are to be designed for the purpose of large-screen television, 
then the balcony should be designed so that the projector can be mounted on the 
front of it at a distance not more than 50 feet from the screen. 

MR. PAUL J. LARSEN: I agree that the front of the balcony is a very nice 
position for the projector, but there is, in my opinion, a very much better place 
where the projector can be placed in theaters without disturbing the seating ar- 
rangements or anything else, and that is by hanging it from the ceiling. It can be 
supported there very rigidly and solidly, and projecting downward to the screen. 
In that way you could have your control box located in the projection room or in 
the balcony, and that would not be taking up any space in the orchestra stalls. 

MR. WEST: That is an interesting point of view. I think that we are rather 
afraid that our roofs are not strong enough to support the equipment. There is 
the question of servicing the projector also. 

MR. LARSEN: It could hang from the ceiling most of the time just like a chan- 
delier, and it could be lowered to the floor by pulley rope when servicing is required. 

MR. WEST: Would not roof vibration cause trouble? 

MR. LARSEN: I do not believe that it would be serious. I do recall some tests 
made some time ago in projecting still pictures that way. Naturally you would 
not depend on a single rope but you may use a triangular rope arrangement which 
would hold it quite steady. 

MR. SCHLANGER: Would not that be in the line of the film projection in the 
projection room? 

MR. LARSEN : You would place it at an angle so that it would not be. 

MR. SCHLANGER: That might require quite a steep angle from the television 
projector to the screen in order to get above the regular beam of the motion picture 
projector. 

MR. LARSEN: It would not be any worse than trying to have it down in the 
orchestra and trying to project it up on to the screen. 

MR. SCHLANGER: That position in front of the balcony that I saw in Mr. 
West's diagram was practically a straight throw. 

MR. LARSEN: That holds true where a balcony is available, but where a bal- 
cony is not available, then the only place you have is in the orchestra stalls, and 
you have to project upward at quite an angle. With my suggestion you could 
project downward. 

MR. SCHLANGER: Every theater will present a separate problem. 



Theater Engineering Conference 

Acoustics 



Auditorium Acoustics* 

BY J. P. MAXFIELD 
VAN NUYS, CALIFORNIA 

Summary This paper presents a review of the factors affecting the 
acoustic properties of auditoria. Emphasis is placed upon not only having 
these factors meet the previously accepted requirements for technical excel- 
lence, but those factors which contribute to the esthetic or dramatic effect, 
particularly as regards shape of the auditorium and the diffusion of reflected 
sound. 

THE DESIGN OF a theater or other place of amusement partakes 
of both the arts and the sciences. The final result must be 
"pleasing" and capable of permitting the performance to arouse, in the 
audience, a maximum of esthetic or dramatic effect. Herein lies the art. 

The mechanisms by which these results are obtained, such as the 
acoustic properties, the clarity of vision, and others, represent the 
factors which are directly amenable to the methods of engineering. 

Fortunately, the correlation between some of the objective factors 
and the esthetic value or "pleasingness" of the artistic result can be 
determined and then can be used to guide the engineer and the 
architect in the best use of the known objective factors. 

The purpose of this paper is to review the acoustics of auditoria, 
with special emphasis on the motion picture theater, and to outline 
the best conditions for the dramatic and esthetic presentation of the 
program. 

Professor Wallace Sabine laid the groundwork for the many later 
developments in architectural acoustics. He studied methods of 
controlling the reverberant characteristics of auditoria and the 
dependence of these acoustic properties on the nature and amount 
of sound absorption present in the theater. 

The introduction of radio broadcasting, electric recording and re- 
production of sound, and later talking pictures gave acoustical engi- 
neers considerable opportunity to study the requirements for "pleasing 

* Presented October 24, 1947, at the SMPE Convention in New York. 

AUGUST, 1948 JOURNAL OF THE SMPE VOLUME 51 169 



170 



MAXFIELD 



August 



acoustics." The "single-channel" transmission, as contrasted with 
normal binaural listening, tended to accentuate all acoustic effects, 
and therefore rendered them more amenable to detailed study. 

The results of such studies indicated that "pleasing acoustics" 
resulted when the following broad requirements were met : 

(1) The magnitude 1 " 3 of the reverberation time and its frequency 
characteristics 4 ' 5 must lie within reasonable limits. 

(2) The first discrete reflections from surfaces close to the source 
must be carefully controlled and dispersed. They should reach the 
audience area from a number of relatively small splays rather than 
from a few large flat walls. 



160 




200 



800 1000 

NUMBER OF SEATS 



1200 



1400 



Fig. 1 



(3) The decay of sound essentially must be logarithmic, but 
modulated by a large number of intensity variations brought about 
by the shifting interference patterns during decay. 

(4) The reverberation should consist mainly of reflections which 
reach the listening position indirectly and with relatively long time 
lapses. 6 

The recent literature regarding requirement (1) is in reasonable 
agreement. 

Requirements (2), (3), and (4) imply the use of means to direct and 
to disperse or diffuse the sound. Volkmann 7 and others have carried 
the idea of diffusion to an extreme by the use of a large number of 
poly cylindrical surfaces. 

In view of the work reported by Hanson 8 in 1931 and the experience 
supporting the desirability of essentially logarithmic decay, the 



1948 



AUDITORIUM ACOUSTICS 



171 



question arises: Is there an optimum amount of diffusion from the 
point of view of "pleasing acoustics?" Hanson showed that a log- 
arithmic decay devoid of fluctuations due to the shifting interference 
pattern did not yield a natural sound. If, however, he modulated 
such a decay with the intensity fluctuations of a shifting interference 
pattern, made up of a large number of small intensity variations, he 
obtained a sound which showed auditorium "character" and was 
"pleasing" to the listener. 

It would seem, therefore, that the time has arrived to examine the 
control of the discrete first-order reflections, the amount and kind of 



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Fig. 2 

diffusion, and the possible desirability of permitting a suitable amount 
of nonuniform distribution of energy among the natural modes of the 
theater to give "character" and "pleasingness" to its reverberation. 

However, there are other important factors in theater design which 
must be considered in producing an esthetically satisfactory audi- 
torium. 

Four of the important factors in theater design are 

(1) The basic shape, which deals with the general relationships 
between the length, the width, and the height. 

(2) The volume or size, particularly in relation to the seating 
capacity. 

(3) The general reverberation characteristic. 



172 



MAXFIELD 



August 



(4) The shape, size, and position of the individual internal sur- 
faces to control the proper distribution and dispersion of the sound. 
NOTE: The four broad requirements apply to the last two factors. 

THE BASIC SHAPE 

Frequently this is influenced by the size and shape of the land 
available as the site of the theater. Fortunately, the acoustic re- 




PLAN 



Fig. 3 New Kleinhaus Music Hall, Buffalo, N. Y. 

quirements allow the architect a considerable leeway in the shape of 
the floor plan. Experience has shown that a ratio of length to width 
which lies between the limits 9 2 : 1 and 7 : 5, when combined with 
proper internal surface design, will yield excellent hearing conditions. 




AUDITORIUM ACOUSTICS 173 

Where the length becomes greater than twice the width the design 
ds to approach the so-called "shooting gallery" shape with the 

ulting difficulties of avoiding multiple reflections between the side 
walls and the high attenuation over the audience heads. On the 
other hand, a ratio of length to width of less than 7 : 5 approaches too 
close to a square, in which a number of the natural modes of the room 
tend to have nearly the same frequencies. 

This statement of limiting ratios does not imply that the floor plan 
should be a rectangle but merely that its general average dimensions 
should lie within these limits. In general, it is desirable to avoid a 
rectangle. 

The ceiling height is largely controlled by the choice of the number 
of cubic feet of volume to be allowed for each seat. However, for the 
7 : 5 ratio of length to width it should not exceed one half the width, 
while for the 2 : 1 ratio it should be less than two thirds the width. 

Having chosen the ratio of length to width and the volume per seat, 
as discussed later, the method of computing the height suggested by 
Rettinger 10 can be applied. 

VOLUME PER SEAT 

For the motion picture theater it is desirable to keep the volume 
per seat low in order to minimize the amount of acoustic treatment 
and sound dispersion necessary. 

Fig. 1, from C. C. Potwin, 1 shows desirable limits of volume in 
cubic feet as a function of seating capacity. These values are based 
on controlling the sound reflections and hence the reverberation by 
proper shaping of the internal surfaces. Regarding Fig. 1, Potwin 1 
says: "These limits have been developed as a result of empirical 
practice, and assume (1) the use of upholstered seats with a spring- 
or rubber-cushioned bottom and padded back, (2) fully carpeted 
aisles, and (3) furred construction of walls and ceiling for low-fre- 
quency absorption. The broken curve is considered generally from 
past experience to be a maximum practical limit for the auditorium 
structure. In most cases a small amount of acoustical material 
properly distributed will be required for these larger volumes." 

Volumes greater than shown by the dotted line tend to result in 
large flat surfaces which must be broken to disperse the sound properly 
and lead away from economy in the planning of the theater. 

GENERAL REVERBERATION CHARACTERISTIC 
The literature covering this phase of design is quite complete and is, 



174 



MAXFIELD 



August 



generally, in good agreement. Fig. 2 shows the reverberation times 
for various frequencies as a function of theater size. This figure sum- 
marizes the data published by Maxfield and Potwin. 5 - 1 

INTERNAL SHAPING 

In rectangular rooms or theaters the sound energy, during decay, 
tends to concentrate in certain well-defined modes of vibration. 




PLAN 





SECTION 



Fig. 4 



While this tendency is less in nonrectangular shapes, some additional 
dispersion is necessary to cause a relatively smooth logarithmic decay. 
This additional dispersion tends to lower the mean free path, that is, 
to decrease the time interval between successive reflections. 

The nature of the successive reflections determines the so-called 
"character" of the theater and the time interval between them is 
interpreted as "size." 

It is generally recognized that when a theater has a "pleasing char- 
acter," the esthetic value of the show performed in it is enhanced. 



1948 



AUDITORIUM ACOUSTICS 



175 



This is particularly true of musical renditions although it also applies 
to speech. 

It follows, therefore, that an amount of diffusion which destroys 
this character may be undesirable since this excess diffusion or dis- 
persion also causes a decrease in the time interval between successive 
sound reflections. Also, it acoustically decreases the apparent size 
of the auditorium. It -has been the experience of the author that too 
much diffusion produces auditoria or theaters which are "character- 
less and cramped" and that such theaters are legs pleasing as places of 
entertainment. 




Fig. 5 



Fortunately, this amount of diffusion is not necessary to obtain 
good definition for speech even when the reverberation time is suffi- 
ciently long for good music production or reproduction. By careful 
internal shaping to reflect the higher frequencies from numerous small- 
angled surfaces on the side walls and ceiling, the definition and "pres- 
ence" can be maintained without using too low a time of reverberation. 

Fig. 3 shows diagrammatically* a plan and elevation of Kleinhaus 
Music Hall in Buffalo, N. Y. The author and the late C. C. Potwin 

* For this figure see Arch. Acoust., Design reprinted from Arch. Forum, September, 
1939. 



176 MAXFIELD August 

believed that the amount of dispersion used in this design represents 
the maximum "sound break-up" consistent with maintaining good 
"character." 

Fig. 4 shows similar diagrammatic sketches* of a motion picture 
theater to which this type of sound diffusion and control of first 
reflections has been applied (Normandie Theater, New York, N. Y.). 

Where the internal shaping can be carried out as completely as shown 
above, for instance, in remodelling an old theater, effective diffusion 
can be obtained by distributing the necessary acoustic treatment in a 
random manner over the walls and ceiling. The use of small absorb- 
ing areas well distributed is superior to the use of a few large ones. 
Completely covering any one wall with absorbing material is bad 
practice. 

Fig. 5 shows a studio t in which most of the sound diffusion was 
odtained by the intelligent random distribution of absorbing material. 

* Also in same Arch. Acoust., Design reprinted from Arch. Forum, September, 

1939. 

t See Fig. 4 of "The control of sound in theaters and preview rooms," by C. C. 

Potwin, J. Soc. Mot. Pict. Eng., vol. 35, pp. 111-126; August, 1940. 

REFERENCES 

(1) C. C. Potwin, "Control of sound in theaters and preview rooms," J. Soc. 
Mot. Pict. Eng., vol. 35, pp. 111-126; August, 1940. 

- (2) P. E. Sabine, "Acoustics of sound recording rooms," Trans. Soc. Mot. 
Pict. Eng., no. 12, p. 812; 1928. 

(3) V. O. Knudsen ; "Architectural Acoustics," John Wiley and Son, New 
York, N. Y., 1932. 

(4) W. A. MacNair, "Optimum reverberation time for auditoriums," J. Acous. 
Soc. Amer., vol. 1, p. 242; 1930. 

(5) J. P. Maxfield and C. C. Potwin, "Planning functionally for good acous- 
tics," J. Acous. Soc. Amer., vol. 2, April, 1940. 

(6) C. C. Potwin and J. P. Maxfield, "A modern concept of acoustical design," 
J. Acous. Soc. Amer., vol. 2, July, 1939. 

(7) J. E. Volkmann, "Polycylindrical diffusers in room acoustic design," 
J. Acous. Soc. Amer., vol. 13, p. 234; 1942. 

(8) R. L. Hanson, "Liveness in rooms," J. Acous. Soc. Amer., vol. 3, p. 318; 
1932. 

(9) C. C. Potwin, "Building Types Section," Arch. Rec., July, 1938. 

(10) M. Rettinger, "Applied Architectural Acoustics," Chemical Publishing 
Company, Brooklyn, N. Y., 1947, p. 75. 

DISCUSSION 

MEMBER: Does the slide that showed the volume per seat still hold? 

MR. JOHN VOLKMANN: Yes, we still adhere to that. It is very desirable to 



1948 AUDITORIUM ACOUSTICS 177 

keep the volume down, but not down too low. You want to obtain enough re- 
flection from the walls and the ceiling to give an enveloping effect of the sound. 

If you make the room too small, below 100 cubic feet per seat, you get the 
ceiling down very low. As was mentioned in the paper, you can get a room that is 
too long relative to the width of the room. You can also have a room that is too 
long relative to its height. Then a number of problems enter into the picture, 
not only the cutting down of the liveness of the room by making the volume 
per seat too small, but you get into the difficulty of projecting enough sound to the 
last rows of seats. 

For all practical purposes, I believe that the analysis that was made from 
that original data still holds. It is a very acceptable guide. 

MR. JOHN K. MILLIARD : It has been our experience where these so-called smaller 
theaters are being operated that there is this feeling of better over-all co-ordination 
of the sound and picture, and we feel that both from the production and reproduc- 
tion standpoint, it is highly desirable to hold the volume down well within these 
shaded areas. 

MR. NEILL WADE: There was a mention of smooth logarithmic decay of the 
sound in connection with the shape of the auditorium. It is still not clear to me 
whether the rectangular shape tends to cause this smooth logarithmic decay or 
whether it is the departure from flat walls which causes this type of decay; and 
second, is this smooth logarithmic decay accepted practice today, or do we find 
that we need something else a departure from that to get 'a pleasing result for 
the listener? 

MR. MILLIARD: I think a departure from the rectangular room is necessary 
for the sake of diffusion; as Mr. Volkmann brought out, and as Mr. Maxfield 
indicated in his paper, it is necessary to provide sufficient random distribution of 
the sound so that reflection from any one surface is small compared to that coming 
from the loudspeaker at the screen. That gives us the so-called presence that we 
talk about and desire, in other words, restrict each individual flat surface down 
to an area where the total energy from this surface reaching the listener in the audi- 
torium is small as compared to that directly from the loudspeaker. 

COMMENT BY MAIL FROM AUTHOR: Mr. R. L. Hanson* has shown, some years 
ago, that a completely smooth logarithmic decay of sound is unpleasant. Ex- 
perience in theaters has demonstrated, however, that the logarithmic decay modu- 
lated by a sound interference pattern consisting of a large number of low-intensity 
modulations produces the most pleasing effect. 

MR. CHARLES LEE: A theater auditorium in which you have a patchwork 
series of absorbing and reflecting surfaces, such as that horrible looking example 
flashed upon the screen, would not be acceptable to the theater audience but it 
might be to the studio recording. I find it very difficult to follow the formulas 
in one theater after another that would yield the ideal results for the auditorium. 
We have had proposed, from time to time, a series of variegated surfaces, and if 
we did use them once or twice, you then are confronted with the architectural 
problem of not having complete repetition for every auditorium. 

CHAIRMAN HARVEY FLETCHER: Are you asking how you can make the audi- 
torium satisfactory when there is a small. audience and also when there is a large 
audience? 
* R. L. Hanson, "Liveness of rooms," /. Acous. Soc. Amer., vol, 3, 1932. 



178 MAXFIELD August 

MR. VOLKMANN: If possible, that means that we should try to keep down the 
variations in absorption in the room as the audience increases. The obvious 
thing is to get seats which are as absorptive as possible, so that when the occupant 
comes in and occupies the seat, he covers up about the same amount of absorbing 
material, you might say, as his clothing contributes to the room. That I think 
is the ideal procedure. That means getting seats that are satisfactory, i.e., that 
have an absorption value of about 3 l / z Sabines. Then the 4.2 units of the person 
do not make a very great difference in the reverberation time. 

CHAIRMAN FLETCHER: Some of you may have been in our little auditorium at 
the Bell Laboratories. When that is full, the characteristics are scarcely any 
different than when you have one person in it, and it is arranged so that the 
seats have the same absorption as the persons when they are sitting in them. 

MR. P. B. ONCLEY: In defense of the last slide which was flashed on the screen 
you didn't read the title at the bottom. That was the photograph of the studio 
before the installation of decorative covering material. It wouldn't have to look 
quite that bad. 

MEMBER: There has been a tendency in the early history of acoustical design 
for theaters to be dictators of what the places are going to look like, and 1 think 
that is what has bothered Mr. Lee and many of us. I think as time went on we 
finally found out pretty much what that slide teaches us, that there are a lot of 
panels in a room. When seen together they certainly are ugly looking, but I 
think the successful method has been to cover them with an over-all masking 
whose appearance is up to the architect. This masking covers both the absorptive 
material and the nonabsorptive surface, so the layman does not know where the 
absorption is at all. 

MR. W. E. MACKEE: We are building a number of theaters of less than 600 
seats, 570 or 580, and our auditorium will be standard. The auditoria will 
be 50 feet wide. The actual seating capacity will be about 90 feet, height 27 
feet. It is costing us, completely equipped, about 115 celnts a cubic foot or $30.00 
a square foot. We have to be careful with our seat spacing, and we are going to 
use 33 inches, and about 15 feet in the back for standing room. 

I am checking up on my architect. I am just asking whether 50 feet wide and 
about 90 feet deep and 27 feet high is an ideal size for a theater of something over 
525 seats, depending on the space between the seats. 

MR. HILLIARD: According to rough calculations, he has 202 cubic feet per seat. 
An over-all average of 18,000 theaters in the United States shows 125 cubic feet 
per seat, so it look,-, as if you have a few more cubic feet than you need for the 
optimum performance. 

MR. MACKEE: These are designed for exhibitors who will not do more than 
$1200 or $1500 a week. When we add one foot to the theater in length, it costs 
us about $6000. We have to watch carefully or the exhibitor will not be able to 
pay us, and we are going to have a theater on our hands. We want to cut it 
down to the limit, otherwise we shall be in the theater business, and we are in the 
banking business. 

MR. E. J. CONTENT: According to Mr. Rettinger's figures, an ideal house for 
600 seats would be a house about 48 feet wide, 88 feet long, with a ceiling 18 feet 
high average. 



1948 AUDITORIUM ACOUSTICS 179 

MR. MACKEE: You are talking about just the seating area? Is the lobby 
included? 

MR. CONTENT: Not including the lobby. 

MR. MACKEE: We are pretty near right then. 

MR. CONTENT: You have too much ceiling height. 

MR. MACKEE : These are one-floor theaters, and the projection room is up on a 
sort of balcony. 

MR. CONTENT: You could drop it enough by proper study, to reduce the 
ceiling height sufficiently to obtain a reasonable cubic content per seat. 

MR. MACKEE : I could knock off $10,000 or $15,000. 

COMMENT BY LETTER FROM AUTHOR: The value of 200 cubic feet per seat is 
definitely too high for best acoustics in a motion picture theater. The author 
agrees with the comments from Mr. Milliard and Mr. Content and believes that 
by lowering the ceiling height materially at the screen end of the theater, and 
properly designing its shape, the situation could be much improved. If the projec- 
tion booth can be lowered, somewhat, without damaging projection, this would help. 

MR. JAMES FRANK, JR: Mr. Volkmann made a remark about the absorption 
characteristics of the seats, that ought to be amplified. There is no question 
that the ideal seat should have the amount of absorption he stated, which I pre- 
sume means a soft covering on both the seat and the back. 

On the other hand, we have to be practical from the point of view of main- 
tenance, and I imagine a very large majority of seats in theaters have an imitation- 
leather covering, at least on the seat portion. We know of course that in the 
smaller and less expensive theaters, they use plywood backs, but a good many 
people insist on imitation-leather covering on the seat. Some people have the 
habit of cutting the covering, and it is easier and less expensive for the theater to 
maintain its seats by recovering with imitation leather than with mohair or some 
other soft fabric. 

However, that is a very definite factor in connection with the acoustical condi- 
tion of the theater. Is it possible to give some relative proportion of a theater 
seat with soft covering on both the seat and the back as compared with an imita- 
tion-leather covering on the seat and a soft back? 

MR. VOLKMANN: Any range from 1.8 to 3.5 does give fairly satisfactory condi- 
tions to meet that problem of variation of reverberation time with an audience. 
The figure of 3.5 I quoted was to obtain as near ideal as possible, with the type 
seats that are available. In other words, a very de luxe house does put in seats 
of that type, but the average is more nearly around 1.7 or 1.8, and in between 
there, 2.5 is another type of seat that is very common in a de luxe type of house. 

CHAIRMAN FLETCHER: What is the absorption value of this imitation-leather 
seat, without the back being covered? 

MR. VOLKMANN : Without the back of the seat being covered, but with a cloth 
upholstering on the back, the value is about 1.8 units. 

With reference to the architect's prerogative of covering the absorbing mate- 
rials, I believe that Mr. Maxfield probably deliberately left off the covering on 
that slide in order not to intrude on the architect's field. Furcher in regard to 
that, I believe the architect has all kinds of opportunities to express the artistic 
phases of his work, in doing more things with regard to these diffusing surfaces. 
There has been a tendency in the studio field, to arbitrarily accept a great deal 



180 MAXFIELD August 

of curve paneling of the cylindrical type, which from the fundamental basis is 
not the only shape that will give adequate diffusion for the reflection surfaces in 
the room, and I should like to make the appeal that the architects do a lot along 
the line of creating designs of conversely shaped surfaces for the diffusing parts of 
the auditorium. 

The other point I wanted to bring out is that many of our calculations on the 
acoustics of the auditorium are based on the reverberation time, but we must not 
forget the echo problems in the room, and the one which gives us the most trouble 
is that the rear wall usually is the most offending surface from the viewpoint of 
echo, and echoes can be very localized to the degree where a few seats in the 
auditorium can be highly disturbed by echo, and the rest of the auditorium will be 
all right. I can think of a number of examples in the theater where we have had 
that kind of problem. 

MR. CHARLES LEE: This touches on a very important item in connection with 
auditorium design, and that is that wherever a soft absorptive material is used 
below the height of five or five and one half feet, children attending the show 
frequently take delight in attacking these surfaces. Can the experts offer any- 
thing other than perforated material, such as we are getting tired of seeing, that 
will give us the reflection and the absorption in the spots that they believe are 
technically desirable, and give us a chance to get them out of the way of the 
young folks? 

CHAIRMAN FLETCHER: Are you asking whether they get a new kind of material 
or a remedy for the children, preventing them from cutting it? 

MR. LEE: I do not think we want either one. We should like to know how we 
can place these materials so we will avoid the reflective spots he cautions against. 

MR. CONTENT: There is very little use in putting absorptive material any 
lower than five or six feet. The space above represents the largest absorptive 
surface in the entire auditorium. Absorptive material should be used on the 
walls above five or six feet and hard surfaces down below. 

MR. P. H. THOMASON: I noticed that Mr. Maxfield's paper omitted the treat- 
ment of the rear wall, that is, backstage areas. Is not that very important to 
obtain good acoustics in an auditorium, where you have the reflection on t 
backstage, also the projection-room ceiling? 

COMMENT BY MAIL FROM AUTHOR: It has been well understood for some yeard 
that the backstage requires some treatment. Frequently the nature of this 
treatment depends specifically on the type of sound system used and its positioi 
on the stage. Therefore it was deemed wiser to leave the specification of this 
treatment to the engineers responsible for the installation of the sound system. 

MR. HILLIARD: There has been no question throughout a number of year 
about backstage treatment. To a person in the audience the sound coming fron 
the loudspeaker should be high and the general reflected sound should be low bj 
comparison. For that reason, it is almost 100 per cent necessary that the back 
stage wall be treated to a very large extent, depending upon the distance or rela- 
tion of the loudspeaker to the rear wall. This avoids what we call slaps. If th< 
loudspeaker were a part of the rear wall, then this damping would not be necessary 
However, the farther out from it the speaker is placed the more drastic must b( 
the treatment. 

MR. WETHERELL: The speaker said that as the stage wall recedes from th( 



1948 AUDITORIUM ACOUSTICS 181 

loudspeaker, more acoustic treatment becomes necessary; as a general rule, 
smaller houses will just allow a little over four feet between the screen and the 
back wall of the stage to take care of the speaker unit. I was wondering whether 
that four feet is enough of a depth. 

MR. HILLIARD: I should consider that some treatment would still be necessary. 
Others feel that this distance might be within the minimum not requiring any 
treatment. 

MR. WETHERELL: Where you have suspended walls, is it not necessary to use 
some sound-deadening material in the back of those walls to keep the walls from 
vibrating? 

MR. CONTENT: Sound-isolation construction? 

MR. WETHERELL: No, furred walls and metal lath and plaster; where you have 
no intermediate supports, more or less a suspended wall, you might say, is it not 
necessary to treat in back of those walls with rock wool or sound-deadening ma- 
terial to keep the walls from vibrating? 

MR. CONTENT: Ordinarily no, they do not vibrate to such an extent, because 
there is enough mass in the lath and plaster to prevent violent vibration. There 
may be some absorption, but it will not be too selective. 

MR. ONCLEY: Mr. Maxfield pointed out that such construction added to the 
low-frequency absorption. 

MR. JOSEPH J. ZARO: Could any of the experts comment on a practice which 
seems to be rather new, of using materials such as we have draped here in this 
auditorium, on furring strips or auditorium insulation, but without any other 
means of sound reinforcement behind the material itself? 

CHAIRMAN FLETCHER: You are asking what effect that will have, or is it de- 
sirable to do it? 

MR. ZARO: Do they have any figures or data on the acoustical value of using 
that material in that fashion? 

CHAIRMAN FLETCHER: Such as this room, without anything back of it? 

MR. BARONIK: Most installations of that type are not too good. The cloths 
that are hung are usually rather sheer, and the absorption that takes place is at 
the high frequencies only. This means that in many of these rooms, especially 
with parallel side walls, you get a booming effect. I do not know how heavy this 
particular material is. In many installations I have seen, you get a booming, 
oarrel effect from that sort of construction, and if you want to preserve more 
iniformity, you should have a material which absorbs more uniformly with 
Tequency. 

MR. BEN SCHLANGER: In the paper given, and in past practice, there has been 
i desire shown by acoustical experts to introduce surfaces and forms near the 
screen which will reinforce the original sound source. This usually leads to a con- 
stricting opening at the picture, and does not allow for future expansion of what- 
iver might happen at the screen end of the auditorium, that is, to get angular or 
xmcave surfaces that will reflect the sound out into the auditorium. You cannot 
lelp but have that go inward toward the optical center of the auditorium. Is this 
practice essential, and could something else be done so that the auditorium can 
>e left as wide as possible at the screen end, with some other approach to the 
>roblem? 

MR. CONTENT: I believe that much work remains to be done in co-operation 



182 MAXFIELD August 

between the acoustics engineer and the architect. The engineer himself cannot 
design a complete theater. He can only say what acoustic materials should go 
into the theater, and if it is not done in absolute co-operation with the architect, 
you do not end up with something esthetically as well as acoustically correct. 
We shall find, by working together with the architect, that we can open up the 
front end of the theater to provide the effect there. 

UNKNOWN: I wonder why the architect would like to have a wide front in the 
auditorium. It seems contrary to my conception; it makes the screen look much 
smaller than it would look if the auditorium tapered down toward the screen. It 
does not provide for extra seats that are of any value. 

MR. SCHL ANGER: I agreed with you years ago, but the reaction from important 
clientele indicates, and I am beginning to believe it myself, that anything that 
tapers toward the picture makes you particularly conscious of the closure and gives 
a constricting feeling, and a more abstract effect is obtainable if you do not ob- 
viously point a funnel toward the picture. 

The specific question was whether the surfaces that we have been introducing 
are absolutely essential to the amount of reinforcement we get out into the audi- 
torium, whether that reinforcement is replaceable by other means which can be 
accomplished. 

MR. VOLKMANN: In the case of sound motion pictures, I refer to Mr. Ryder's 
comments this morning; he advocated treating the whole front proscenium area 
with absorptive materials and making the live end of the room in the rear. In 
the case of sound motion pictures then, where you have amplification, you can 
eliminate the necessity for the side walls, if I have understood you. 

MR. SCHLANGER: That is a new approach, because it has been in the other 
direction. For years we have been told to reinforce the sound at the screen end. 

CHAIRMAN FLETCHER: May that not be an economic problem, if you have to 
use four or five times as much power to get the sound out there; if you put ab- 
sorptive materials back there and do not have this reflection you see that prob- 
lem comes into it too. That is what you would have to do. 

MR. HILLIARD: About ten years ago, there appeared in literature material in 
which considerable emphasis was placed on getting the architect to make the 
surface convex instead of the customary concave, and we still believe that this is a! 
very potent factor. By making the surface adjacent to the screen diffusing, we 
can still build up the sound level in the auditorium, but we do not create the 
focal points that were present in some of the earlier types of construction where 
the curvature was concave. Since then many theaters have been built with the 
surface curved so as to diffuse the sound. We have had excellent results, and I 
believe that as an architect you will find that there are many, many ways in which 
you can accomplish this" purpose and still maintain the objective that we are 
seeking. You can do it with small curves, large curves, and decorate it in a man- 
ner so that it does not look like a funnel. You can blend that in with the front 
part of the auditorium, so the audience does not appreciate that it is being done. 

MR. ONCLEY: Most of the talk has centered around the motion picture thea- 
ters. This is a very special problem. However I think we might point out that 
in many of the music halls, especially the opera halls of Europe, you have good 
acoustics with stages as wide as the whole front of the theater, stages as deep as 



1948 AUDITORIUM ACOUSTICS 183 

the whole body. I should not think it would be necessary, in fact, to have a nar- 
row stage in the moving picture theater. 

COMMENT BY MAIL FROM AUTHOR: The author notes with interest the remarks 
by Mr. Ben Schlanger. It is true that in theaters and auditoria in which no 
sound-reproducing or amplifying equipment is used, it is important to shape the 
stage end of the theater to aid sound reinforcement in the audience area. 

There are two reasons why the author has recommended the narrow front, in 
the past, for motion picture theaters. First, it is of material assistance in obtain- 
ing a low value of cubic feet per seat. Second, he believed, as Mr. Schlanger says 
he once did, that the architects desired that form for esthetic reasons. 

There is no definite acoustic requirement for narrowing the theater at the 
screen end where sound-reproducing or amplifying systems are employed, but it is 
highly undesirable to obtain this breadth by employment of front-wall surfaces 
which are concave toward the auditorium. Also, by the proper shaping of these 
end-wall surfaces it becomes unnecessary to use large amounts of sound-absorbing 
treatment on the walls immediately adjacent to the screen. 



Theater Engineering Conference 

Acoustics 



Quieting and Noise Isolation* 

BY EDWARD J. CONTENT 
STAMFORD, CONNECTICUT 

Summary The purpose of this paper is to describe some of the ob- 
jectionable noises, their causes, some of their remedies, and to point out 
that it is much easier to avoid these troubles in building a new theater than to 
rectify them in an old one. 

NOISE is ANY undesirable sound, but all sounds do not have the 
same effect on a person, and low tones, of course, are not nearly 
so objectionable as higher tones. Howard Hardy recently said in 
The Frontier: "A sound source of many component fragments will 
sound much louder than one of the same intensity which has a pure 
tone." Considerable confusion exists among inexperienced ob- 
servers about the particular psychological factors with reference to 
noise. It has been shown that noise of a frequency below 500 cycles is 
not nearly so objectionable as noise consisting of high-frequency tones 
and harmonics. 

The object in noise reduction in design is to shift the objectionable 
sound from high to lower frequency, as well as to lower its intensity. 
Loudness alone is not an indication of the annoying effect. People 
do not object to noisy machinery as much as to erratic and unex- 
pected sources of sound. Such things as high-frequency screeches 
are definitely more disturbing than the low frequency of thuds or all 
the lower tones. 

There is no doubt that high noise levels in theaters require the 
operation of the sound system at a higher level, and even though the 
audience does not realize that the sound level is higher than other-; 
wise would be the case, it does put them under a nervous tension, and j 
if the noise is extremely high, the sound level has to be so much higher j 
to overcome the noise that it really becomes annoying. 

There are several misconceptions that should be explained. Many i 

* Presented October 24, 1947, at the SMPE Convention in New York. 
184 AUGUST, 1948 JOURNAL OF THE SMPE VOLUME 51 



QUIETING AND NOISE ISOLATION 185 

people do not differentiate between sound isolation and acoustical 
conditioning. Sound isolation fundamentally consists of two things 
soundproofing of solid-borne noises such as shocks and machinery, 
and the sound insulation of air-borne noises such as is provided by 
thick walls and special construction, which prevent the sound from 
being transmitted from one point to another. 

On the other hand, acoustical conditioning consists of three factors, 
the control of the reverberation time, controlled by the amount of 
sound-absorbing material used; the control of reverberation charac- 
teristics determined by the type of materials, and how they are used; 
and by the elimination of sound focal points and standing waves, 
which is done by the elimination of opposing parallel and concave 
surfaces. 

As stated above, all of these faults are much more easily avoided 
in new construction than cured in old construction. Wherever a 
theater is to be built, a noise survey of the site is absolutely necessary 
to determine the noises in the surrounding area. Outdoor and traffic 
noises in some areas may reach 85 to 90 decibels above zero reference 
sound level of 10~ 16 watt per cubic centimeter. 

The noise in the theater itself should be kept to a point where it is 
lower than the audience noise (a good value of audience noise is about 
30 to 35 decibels) , which means that the outside walls of the theater 
may be required to have an insulation value of 55 to 60 decibels, which 
if dependent upon mass alone, requires a brick wall two feet thick. 
Fortunately there are other ways of doing this by special construction 
which is much less costly than a two-foot brick wall. 

There are some noises that are not under the control of the archi- 
tect and engineer, such as street noises caused by automobiles, bus 
traffic, airplanes, railroad trains, streetcars, subway and elevated 
trains, and garbage and ash collectors. 

Of course, there are audience noises about which nothing can be 
done, except hope for a quiet audience. There may also be noises 
from adjacent property music, loudspeaker systems, juke boxes, 
hand trucks, factory operations, and about the noisiest source is a 
bowling alley. 

Windows have no place in the theater, as they are always weak 
points in any wall which allow sound transmission. If there must 
'be windows they should be fastened so they cannot be opened, to 
reduce sound transmission. In some cases, where there is noise on 
adjacent property such as floors above or below the theater, it may be 



186 CONTENT August 

necessary to construct isolated ceilings and floors, and even isolated 
suspended walls, as in broadcast T studio construction. 

Of course, there must be fire-escape doors, which should be fitted 
tightly to provide as good sound isolation as possible. This also 
helps in the operation of the air-conditioning system. 

A good example of noise isolation occurred at radio station WOR, 
with studios on the first floor, where there was a corridor at the rear 
which led from the street to the freight elevators. Many times during 
the day there were deliveries by hand trucks which were very noisy 
and interfering noises were heard in the studios. The solution was 
surprisingly simple. About an inch and a half of street-paving as- 
phalt was laid on the floor of the corridor, which eliminated that 
noise in the studios. 

There are a number of controllable noises in a theater. First there 
are the noises from the projection, the rewind, and generator rooms. 
The best insurance there of course is to specify and get quiet operating 
machines. As Mr. Hardy has reported in another paper, the acoustic 
problem is being thoroughly considered in the manufacture and design 
of projectors. The ceilings of these rooms should have noise-reducing 
treatment, such as fireproof acoustical tile, or some kind of fireproof 
treatment having as high a value of sound absorption as possible. 

If the ceiling is high, acoustical absorbing materials should be used 
on the walls also; to four or six feet from the floor. The projection 
ports should be fitted with optical glass. However, as that represents 
another maintenance problem, another way that the noise can be 
retarded from getting into the auditorium is by lining the top and 
sides of the ports with acoustical tiles. The viewing ports should be 
fitted with plate glass which reduces the amount of transmission 
through these openings. 

Another source of noise is noisy electrical equipment. The only 
precaution required is to buy good equipment, making sure that it is 
operated in the most efficient manner by engaging the services of an 
organization thoroughly competent in maintenance of sound equip- 
ment for the theater, to maintain the equipment. There are reliable 
organizations which provide that service. 

Other noises originate in the lobby, the promenade, the ladies' 
and men's lounges, and the rest rooms. The ceilings of all these spaces 
should be treated with noise-reduction materials with carpets on all 
spaces except the rest rooms. 

The ventilating systems are sources of noise such as motor or fan 



1948 QUIETING AND NOISE ISOLATION 187 

noises, which can be both air-borne and solid-borne. One airborne 
noise is the noise of the air itself in rushing through the ducts and 
grills, and the solid-borne noises can be caused by the vibrations be- 
ing transmitted through the ducts. 

The best insurance against these noises is to operate an air-condi- 
tioning system so that the air in the ducts flows at low velocity. At 
the registers, both supply and return, the air velocity should not exceed 
250 or 300 feet per minute. Metal registers, where the metal is 
placed edgewise, are also a source of noise. At the higher air velocity 
the fins may begin to vibrate. It is best to use a flat punched register, 
with at least 50 or 60 per cent opening so the air is not constricted, and 
will not appreciably increase in velocity in the openings. 

In one theater which had air noise in the ducts, the trouble was 
corrected by putting in sound baffle boxes, sound traps, in the branch 

! ducts just before they went to the inlet registers. In this manner it 

i was still possible to get a sufficient amount of air with the existing 

|j motor and fan. 

In a new system, install low-speed, quiet operating fans because 

:j high-speed fans are prone to greater and higher frequency noises. 

Another cause of noise is the water-supply system, such as knocking 

in the pipes when a faucet is turned on, and there may be vibration 
in the pipes, especially with copper and brass pipe. The proper way 

I to prevent the knocking is to have the proper air cushions installed in 

; the pipes and to make sure the valves seat properly. 

Water lines can be fastened in shock-absorbing mounts so that 

I* vibration will not be transmitted to the theater structure. The 
troubles encountered in a hot-air system are very much the same as in 

I ventilating. A hot-water heating system is like any other water 

|: system, but with steam heat, hissing valves should be replaced with 
quiet operating vent valves on the radiators. A big source of noise 
is steam systems is in the pressure-reducing valves. In one installa- 

|i tion the noise was as high as 90 decibels within a foot or two of the 
valve. The valve and steam-pipe line causing the noise and vibration 
were isolated from the rest of the building to prevent transmission of 
structural-borne noises and covered with alternate layers of various 
materials to reduce the noise in the rooms where the pipes and valves 
were located. The pipes on both sides of the valve should be hung in 
shock-absorbing mounts for sufficient distance, so the vibration will 
not be transmitted to the rest of the structure. 
The rest rooms should be separated from the auditorium by at 



188 CONTENT August 

least two walls, not necessarily two walls built together, but at least 
two walls separating the rest rooms from the audience. 

Other sources of trouble are noisy reactors and transformers for 
fluorescent and cold-cathode lighting. Wherever these are noted, 
they should be corrected. Noisy electric switches cause clicks at 
times, which can be eliminated by replacement with mercury switches. 
Oftentimes vibrations are set up by different kinds of machinery, 
motors, pumps, forced-draft fans, oil burners; they should all be lo- 
cated on antivibration mounts to prevent the vibration from being 
transmitted to the building structure. Quite often this vibration will 
set up very serious noises in some other part of the building. 

If there are any elevators in the same building, all the machinery, 
the hoist drums, the controllers, the contactors, the motors, should 
all be hung on vibration-isolation mounts, and the guide rails for the 
elevators should be mounted on antivibration mounts. 

A certain amount of trouble is caused by concavity of rear walls in 
theaters. Oftentimes domes and other concave surfaces catch sounds 
and retransmit them to other points, sometimes louder than they were 
in the original location. The answer is to eliminate the use of concave 
surfaces if possible. If it is necessary to use concave surfaces, make 
sure that the distance from the focal point to the concave surface is 
either at least twice or Jess than one half the distance to the populated 
area of the theater. 

In one theater the author collaborated with Mr. Schlanger in re- 
vising the acoustical treatment. In this theater having this trouble 
the dome was eliminated and replaced with a flat ceiling. 

In conclusion two points should be emphasized for either new 
construction or for alteration ; one, engage the services of a registered 
architect who has had experience in theater construction as there are 
points that the average architect will never encounter; two, always 
see that he engages the services of a competent acoustical engineer. 

DISCUSSION 

MB. W. E. MACKEE: Seat men think the most important thing is a seat. The 
carpet man thinks carpet, is most important. The man who sells lighting tells 
you how to light your theaters. The acoustical people say the most important 
thing is acoustics. I think you have forgotten the real purpose of a motion 
picture theater. 

First you must understand that there is a different type of audience in the small 
motion picture theater today. Sixty per cent of these have less than 500 seats, 
and 74 per cent have less than 750 seats. What is a motion picture theater? 
Before the war the average audience was supposed to be 19 years of age and pic- 
tures were made for them. Then the war started, and exhibitors thought they 



1948 QUIETING AND NOISE ISOLATION 189 

would go out of business for our younger people were all going to war. As a matter 
of fact, we did more business. We got an entirely new audience; older people 
are going to the movies, discovering the movies. The average is 32 or 33 years 
of age. They go more often and they pay more, that is our audience today. 
Why do they go to see motion pictures? 

They go primarily for two reasons, rest and recreation. They can stay home 
and listen to the radio; incidentally radio audiences have dropped, and motion 
picture audiences have increased. They are not staying home and listening to 
the radio. We draw these facts from the radio industry. The motion picture 
audience of today is composed of older people. They demand a different type of 
picture than we had before the war. 

What comes out of the radio? Charlie McCarthy. Charlie McCarthy is not 
successful in motion pictures. One picture that brought all the people in is one 
you probably do not remember "Mrs. Miniver." It was not designed for the 
19-year-old audience. It was designed for older people. Just about that time, 
the audience aged. More people are coming in and they are staying in. 

In the motion picture industry we have to bring them out of their homes. 
You have a nice living room, and you have your radio and your family, but you 
go a mile or five miles to a motion picture theater. Why do you do that, and pay 
real money for it? You do that because the modern theater today is just as good 
as your living room. The seats are very comfortable, and the most important 
thing in the theater is not sound. The most important thing is the picture image, 
going back to the fundamental purpose of the motion picture. Sound is secondary. 
In the pictures that come to us, too often sound predominates, but the audiences 
go for rest and recreation and a series of pictures flashed on the screen. Sound is 
just explanatory. Anything you can do to remove your noises is desirable, but 
do not forget that the motion picture basically is a series of photographic images 
flashed on the screen. 

DR. RICHARD COOK: Recently in Washington the picture was flashed on the 
screen, but for some reason the sound did not come on. There were catcalls from 
the audience, "Where is the sound?" They wanted sound right away. 

DR. E. W. KELLOG: All we try to do in the way of better sound is to improve 
the value of the theater for seeing the pictures. 

MR. M ACKEE : We do not want newsreels in the small theaters. The football 
pictures are full of sound and noise. We can do without a newsreel. We keep 
sound down as low as we can. Air conditioning, yes; and quiet, yes; and a nice 
comfortable theater. We do not say you should eliminate sound, but we definitely 
are finding out what these older people want, and that is the most important thing 
as far as dollars and cents in the box office are concerned. 

MR. JOHN K. HILLIARD : Why is it, especially in a dramatic sort of picture, when 
the sound is low, the audience is sitting there listlessly, and if the sound is brought 
to the proper intensity, not necessarily loud, the audience immediately reacts 
and applauds a scene, where if the sound were below what it should have been, 
there is absolutely no reaction from the audience. 

MR. MACKEE: If it is so low they cannot hear, they start to clap. If they 
can hear, we do not hear any comment. Some theaters have earphones. We 
could not understand why people would put on earphones when they are not deaf. 
We asked one or two, and they said it was because they can control the sound. 



190 CONTENT August 

MB. LEONARD SATZ: Sound is so much a part of motion picture presentation 
that I do not see how you could improve one without improving the other. Maybe 
some prefer to call it intangible, but when a patron comes into the theater and 
sits down, it is primarily to enjoy himself. If the sound is not good, he will leave 
the theater. He does not want to strain to hear the words. We consider sound 
in the smaller theaters just as important as in the larger theaters. 

MR. GONZALEZ: During the war, we operated 1200 theaters.' We had up- 
wards of 12 to 14 theaters in some installations. We put in proper acoustic 
material, with the proper absorption, and someone painted the material with 
oil paint. Where there was reverberation, the sound was distorted. We found 
that at these places where the sound was improper, the soldiers would walk a 
half mile or a mile to go to a theater that had good sound, and attendance at the 
improperly wired theater fell off, which proves that we needed good sound. 

Mr. Content said that the recirculating velocity should be limited to 250 feet per 
minute, and that the duct be limited to 500 feet. That is rather expensive in 
design. We found that we could safely go as high as 1200-foot velocity without 
interfering with the sound system in the theater. So long as the duct was prop- 
erly designed so that there were no abrupt changes of air to cause sound or air 
noises in the supply grills, we went as high as 600 feet velocity without any per- 
ceptible increase in the noises. 

MR. WETHERELL: When I design a motion picture house one of my main in- 
terests is in the appearance of the finished product and its effect on the viewer. 
I wonder if there is not one point that has not been touched on concerning sound. 
Someone mentioned that sound is secondary. It seems to me it might be, to this 
extent. The aim of the acoustics and sound engineer should be to produce sound 
that is so natural it becomes the background of the picture. You come to the 
theater, you see the picture, the sound is woven around the action. It should be 
so natural and so keyed that you do not realize you are listening to artificial sound. 
It is not the aim to have sound so natural that perhaps it is secondary, but 
it is quite an art to produce sound that is natural and accurately follows in tone 
and volume the action. 

Mr. BEN SCHLANGER: I want to defend what the paper said about air noises. 
There are certain dramatic sequences where the words are spoken softly and 
during those periods air noises are very disturbing. Maybe in the louder se- 
quences I do not mean noise but higher levels and less dramatic air noise 
may not be disturbing, but you have to design for the more particularized 
mood in the picture once in a while. 

MR. E. J. CONTENT: There are parts in the picture where sound levels will 
reach as high as 80 or 90 decibels, and certain parts which will be of low intensity 
as low as 30 or 35 decibels. If you have noises masking the sounds, they are not 
producing the desired effect upon the viewer. The only way you can keep back- 
ground noises to 30 or 35 decibels is to operate the air-conditioning system at low 
velocity as mentioned. 

MR. D. G. BELL: We have the main trunk lines approximately 700 feet per 
minute in the lines to the outlets. The principal noise from the duct system usually 
originates in the fan, in the blower, and it has been necessary in many other 
cases to add an acoustic absorbent in the duct for ten or twelve feet after the 






1948 QUIETING AND NOISE ISOLATION 191 

blower in the duct, immediately after the blower; and using those velocities which 
are recommended by the American Society of Heating and Ventilating Engineers, 
we have kept the noise in the theater down to 30 and 35 decibels. 

MB. SHEPABD: I believe the point that Mr. Gonzalez brought out may not 
have been followed perfectly. He wanted to.show that by proper designing, you 
can have fairly high velocity without the introduction of noise which can be gen- 
erated by any vibrating element in the system. It can be reduced by the proper 
construction, the proper handling of beams, and possible use of acoustical materi- 
als. In many of the installations in the theaters that I have visited where that 
was done, I do not know what the actual velocities were but they were fairly high, 
and the noises were not excessive; just where you would have to obtain the maxi- ' 
mum velocity, I do not known. 

MR. SGHLANGER: It is ridiculous to try to save a few dollars by using a higher 
velocity than you should when you have already invested so many thousands of 
dollars in a theater. 

MR. SATZ : Do you have any special preference for slab cork for vibration elimi- 
nators, cement pit with cork, for heavy fans; would you say that one is more 
efficient than the other? 

MR. CONTENT: That all depends on the weight of the machine, the frequency 
of the vibration, and other factors, such as the weight of the noise-making parts. 
The isolating material must be loaded to a point where the transmission of the 
vibration through the material is very low. It is possible to use vibration mounts 
where there will be more vibration transmitted than if there were no isolation at 
all. Each individual problem must be analyzed carefully. 

MR. SATZ : Ho you find that glass fabrics are any less suitable than cotton? 

MR. CONTENT: I see no reason to condemn one as against the other. Sound 
will transmit through the glass fabrics, through the pores as well as through the 
cotton or other materials. Sound as we hear it is a movement of air, and it will 
get through the pores of the glass cloth just as well as the cotton. 

MR. A. D. PARK: What is the recommended treatment for the rear wall of a 
motion picture theater? 

MR. CONTENT: The best treatment for a rear wall is not to make it concave. 
Break it up. If you do that, you may not need sound-absorbing material. All 
you want to do is to prevent echoes which are reflected from the rear wall from 
reaching the audience. If that wall disperses sound sufficiently so it will not 
produce echoes, if it is a concave surface, you must use an absorptive material 
with a high coefficient, so that very little sound will be reflected back to cause 
trouble in the audience. 

MR. JOHN VOLKMANN: It depends considerably on how far the rear wall is 
from the seating area, that is, the front of the room. In certain seating regions, 
it is possible where, in addition to shaping the walls, you have to put a lot of 
absorptive material on it too. I know of cases where we have had a lot of ab- 
sorbing material on it, and we had to angle the rear wall down, as well as treat it, 
purely because the surfaces which, as I say, were treated with rock wool, per- 
forated and paneled and cloth-covered on top of that they were so disposed that 
they were on a curved surface, and because they were so disposed, they tended to 
concentrate the sounol into localized regions and not until we angled them for- 
ward did we get rid of the concentration effect. 



Theater Engineering Conference 

Acoustics 



Behavior of Acoustic Materials 

BY RICHARD K. COOK 

NATIONAL BUREAU OF STANDARDS, WASHINGTON, D. C. 



Summary Theater architects and engineers need accurate data on 
the performance of acoustic materials, which are used to control the acous- 
tics of theaters. Descriptions of prefabricated materials and acoustic plas- 
ters are given. The mechanism of the sound-absorption process in por- 
ous materials is briefly described. There are two commonly used absorption 
coefficients, the "random-incidence" coefficient, and the "normal-incidence" 
coefficient. The experimental methods used for measuring the two coeffi- 
cients are described. The significance and limitations of these coefficients 
hi theater design are pointed out, and it is concluded that, at the present 
time, the random-incidence coefficient is more useful in auditorium design. 
Recommendations for painting acoustic materials are made, and illustra- 
tions of the results of painting are included. 



THE CONTROL OF THE acoustics of auditoriums and theaters, and 
the quieting of noisy rooms, both require the installation of 
acoustic materials. By an acoustic material is usually meant a 
sound-absorbent substance which is fastened in flat patches to the 
walls and ceiling. Recently, however, some absorbers have been 
fashioned in the form of cylinders, cones, and spheres, and have been 
suspended at a distance from the walls and ceiling of the room. 

The principal function of acoustic materials is to absorb sound en- 
ergy which originates within the room. Only incidentally do they pre- 
vent the transmission of sound energy from one room to another. 
Such transmission is better prevented by other techniques. 

Architects and engineers are faced with the problems of deciding 
what material should be used in an auditorium to secure the proper 
amount of sound absorption, and deciding what is the most econom- 
ical absorbent to quiet a noisy location. It is clear that they must 
have accurate data on how acoustic materials absorb sound. Such 
data have been available for many years. 1 However, the special 
uses to which a material is put will in general require more detailed 
* Presented October 24, 1947, at the SMPE Convention in New York. 

192 AUGUST, 1948 JOURNAL OF THE SMPE VOLUME 51 






1948 



BEHAVIOR OF Acoustic MATERIALS 



193 



information than can be obtained from the results of routine labora- 
tory tests. Nevertheless, the results of such tests are of great im- 
portance to the theater engineer, and he should understand their 
significance and limitations. 

II. DESCRIPTION OF MATERIALS 

There are two main kinds of acoustic materials. One kind is pre- 
fabricated, a familiar example being the one-square-foot tiles which are 
commonly used in many public places. The other is the kind which 
is manufactured, so to speak, at the moment of application, and in- 
cludes acoustic plasters and sprayed-on fibrous materials. 

There are various types of the prefabricated kind. A common type 



SOUND 



SOUND 



PERFORATED 
FACING 



PORES 




Fig. 1. Some types of acoustic materials. 

is the homogeneous porous absorbent consisting of wood fibers, or 
glass fibers, or granulated material, held together with a suitable 
binder. Another common type is the porous material having a hard, 
nonporous surface which is perforated (Fig. 1) so that the sound waves 
can pass into the porous region and be absorbed. The perforations 
might be regularly spaced slots, or circular holes, or irregular fissures. 
Another type is the porous material installed in blanket form, such 
as glass wool or rock wool, and protected by a perforated surfacing of 
wood, metal, or asbestos cement board. The principal advantage of 
the prefabricated acoustic material lies in the uniformity of the prod- 
uct. The manufacture can be carefully controlled, and in general 
there are relatively small variations in the absorption coefficients for 
a particular type. 



194 -COOK August 

Several different types of acoustic plasters are available. Some 
consist of granulated inorganic substances which are mixed with a 
foaming agent and a suitable binder, and are applied with a trowel. 
Sometimes the plaster is stippled (in order to improve the absorption 
of sound) before it has set hard. Other types consist of fibrous mate- 
rial, usually rock wool or asbestos, which is mixed with a binder and 
sprayed directly on to the wall by means of special equipment. 
Acoustic plasters are generally difficult to handle, and careful control 
must be exercised when they are applied. Occasionally, however, 
there are economic advantages in favor of plaster and sprayed-on 
materials. 

A third kind of acoustic material has been used in Europe, and 
consists of sponge rubber having a low modulus of elasticity, and 
covered with a thin impervious skin. Such absorbents do not seem 
to be commercially available in this country. 

Acoustic materials can also be classified by the way in which they 
absorb sound (Fig. 1). A knowledge of the mechanism of absorption 
is important, especially if one is going to be faced with the problem of 
painting the material, or keeping it decorated. In almost all cases, 
the absorber is porous, and the absorption of sound is due largely to 
the viscous damping of the motion of molecules of air in the pores. 
Sometimes the absorption process is aided by vibration of the porous 
material itself. In addition, the propagation within a porous material 
is influenced by the tortuousity of the channels .(see the sketch to the 
right in Fig. 1) and by thermal effects. In fact, it is difficult to say 
which absorption mechanism predominates in a given porous ab- 
sorbent without conducting a complicated investigation as to how 
sound is propagated through a material. The sponge rubber de- 
scribed earlier absorbs sound by frictional damping in the rubber. 
Oddly enough, some very soft and porous fibrous materials, after 
being covered with an impervious layer of paint, behave like sponge 
rubber. As a general rule, however, it is very important to preserve 
the porosity of an absorbent. This makes painting difficult, a point 
which will be discussed.later. 

III. MEASUREMENT OF ABSORPTION COEFFICIENT 

A number of elements are important in the choice of an acoustic 
material. The user is interested not only in sound absorption, but is 
also concerned with light reflection, fire resistance, appearance, 
strength, and paintability, all of which are important. However, we 



: 



1948 



BEHAVIOR OF ACOUSTIC MATERIALS 



195 



shall discuss only the measurement of sound-absorption coefficients, 
and the influence of painting on acoustic properties. 

Suppose a beam of sound waves is incident upon an acoustic mate- 
rial. The beam carries power. The absorption coefficient is the frac- 
tion of the power which is absorbed. For example, if a material ab- 
sorbs 65 per cent of the sound power incident on it at 512 cycles per 
second, the absorption coefficient at this frequency is 0.65. An im- 
portant point is that the absorption coefficient depends not only on 
the physical properties of the material, but also on how it is mounted. 
As a general rule, an air space between the absorbent and the rigid 
wall on which it is mounted enhances the absorption. 

Physicists and engineers have struggled long with the problems 
of how to define better and how to measure the absorption coefficient 

ACOUSTIC _ 

MATERIAL"/ SHORT TuB 




VIBRATING 
DIAPHRAGM 



Fig. 2 Impedance tube for measurement of normal- 
incidence absorption coefficient. 

of a material. In Fig. 2 is shown a technique for measuring absorp- 
tion when sound is incident normally, i.e., perpendicularly, to the 
surface. The source is a vibrating diaphragm located to the right 
in the diagram. The acoustic material is to the left. By measuring 
the sound pressure at the center of the surface, we can deduce, from 
a knowledge of the amplitude of vibration of the diaphragm, what 
the absorption coefficient is for sound at normal incidence. Varia- 
tions of this technique have been used. Sometimes the standing- 
wave pattern in the tube is explored with a probe tube and micro- 
phone. The important thing is that the general idea is always the 
same, namely, we measure the absorption coefficient when sound is 
incident perpendicularly on the surface. The coefficient obtained in 
this way is called the "normal-incidence absorption coefficient." 



196 COOK August 

The basic idea of the other technique which is extensively used for 
measuring absorption is to have the sound incident on the material 
from all possible directions. To achieve this, the material is placed 
on the wall or floor of a large, highly reverberant room. Sound of 
the desired frequency is introduced into the room, and the distribu- 
tion of sound energv is "randomized" by any one of several ingenious 
methods. This means that sound rays strike the surface equally 
from all directions. When the sound field has become thoroughly 




Fig. 3 National Bureau of Standards reverberation 
room. Used for measurement of random-incidence ab- 
sorption coefficient. 

randomized, the source is turned off, and the rate of decay of the 
sound energy is measured with microphones and a recorder. The ab- 
sorption can be deduced from the measured rate of decay. The co- 
efficient obtained with this technique is called the "random-incidence 
absorption coefficient." 

In Fig. 3 is shown the 15,000-cubic-foot reverberation room at the 
National Bureau of Standards. The sample, which is usually 72 
square feet in area, is on the floor. The loudspeakers which supply 
the sound are on the vanes. The vanes rotate while measurements 



1948 



BEHAVIOR OF ACOUSTIC MATERIALS 



197 



are being made, and help to randomize the sound field. The micro- 
phones which pick up the sound are not shown. 

The important question is, how significant are the normal-incidence 
and random-incidence absorption coefficients in practice? As was 
pointed out earlier, the principal use of an acoustic material in an 
auditorium is for control of the reverberation time. Many years of 
experience seem to show that the reverberation time can be com- 
puted correctly if the random-incidence coefficient for the acoustic 
treatment in the auditorium is used in the calculations. On the other 
hand, it is not really necessary to design a motion picture theater for 
optimum reverberation time. The loudspeaker system can supply 
ample acoustic power, and hence large amounts of absorption can be, 
and usually are, installed in a motion picture theater. Even though 




Fig. 4 Simplified geometrical acoustics of an 
auditorium having a sound-absorbent ceiling. 

the normal-incidence absorption is more easily determined in the 
laboratory, it is still difficult, and in some cases it is impossible, to 
deduce the random-incidence behavior from laboratory measurements 
with normally incident sound. On the whole, the conclusion at the 
present time is that the random-incidence absorption coefficient is 
more useful in auditorium design. 

Some of the difficulties involved in deciding how to measure sound 
absorption can be appreciated by referring to Fig. 4. The sketch 
shows that the listener receives sound which is non-normally reflected 
from the acoustically treated ceiling. If one wishes to compute the 
intensity of the reflected sound, neither the normal incidence nor the 
random incidence coefficients can be used! To make matters worse, 
the angle "6" of the reflected sound is different in different parts of the 
auditorium. The object in pointing out these things is to indicate 



198 COOK August 

the limitations on the absorption coefficients when an acoustic mate- 
rial is being chosen for a theater. 

IV. PAINTABILITY OF ACOUSTIC MATERIALS 

Since the majority of commercially available acoustic materials 
depends on porosity for sound absorption, it is clear that painting 
will present a problem. There is always the possibility that excessive 
painting will clog the pores and prevent absorption of sound. 

In the case of porous materials having a mechanically perforated or 




Fig. 5 Fissured surface of a porous Fig. 6 Same material as in Fig. 5 
acoustic material. after application of four coats of brush- 

applied paint. 

fissured facing, there is no serious difficulty. Paint can be applied 
so long as the perforations and fissures remain open. 

The painting of a porous material without large holes or fissures 
is more difficult. The paint must be applied as thinly as possible, 
preferably with a spray gun. If it is brush-applied, care must be taken 
to thin the paint and to get it on the surface without closing the pores. 

The nonporous rubberlike materials can be painted, provided the 
paint does not substantially increase the weight of the facing. Too 
much paint will reduce the absorption of sound at high frequencies. 

The effect of painting on some typical porous materials can be seen 



BEHAVIOR OF ACOUSTIC MATERIALS 199 

from the following data obtained from a paper by Chrisler. 2 Fig. 5 
shows a fissured material which had a noise coefficient of 0.55 before 
painting. The noise coefficient is here defined as the average of the 
random-incidence absorption coefficients measured at frequencies of 
256, 512, 1024, and 2048 cycles per second. Fig. 6 shows the same 
material after it was brush-painted four coats. The noise coefficient 
fell to 0.45 after painting, which is not a serious reduction. The 
reason for the success of the brush painting is that the material was 
fissured. The fissures which lead down into the porous material 




Fig. 7 Granular surface of a porous Fig. S^Same material as in Fig. 7 
acoustic material. after application of five coats of brush- 

applied paint. 

were not covered over, and a considerable amount of sound ab- 
sorption remained after painting. 

Fig. 7 shows a porous material consisting of organic and inorganic 
granules held together with a binder, and having a granulated sur- 
face. Before painting, the noise coefficient was 0.60. Fig. 8 shows 
the same absorbent after five coats of brush-applied paint, when the 
noise coefficient fell to 0.25. This is a too-familiar horrible example 
of bad treatment of an acoustic material. The method of painting 
in this case should have been either with a spray gun, or with a 
thinned paint carefully brushed on so as not to close the pores. 



200 COOK August 

REFERENCES 

(1) The results of tests made at the National Bureau of Standards have been 
published in its Letter Circular LC-870, "Sound Absorption Coefficients of the 
More Common Acoustic Materials." 

(2) V. L. Chrisler, "Effect of paint on the sound absorption of acoustic mate- 
rials," J. Res. Nat. Bur. Stand., vol. 24, p. 547; RP 1298, 1940. Reprints may 
be secured for 10 cents from the Superintendent of Documents, U. S. Government 
Fruiting Office, Washington 25, D. C. (stamps not accepted). 

DISCUSSION 

MR. WETHERELL: What difference in effect do you obtain with varying per- 
centages of opening, or holes in the surface? The area of the holes forms a very 
small percentage of the total area. What is the difference in efficiency for dif- 
ferent percentages of opening? How does that work out? 

DR. RICHARD COOK: So long as the area of the slots or holes is ten per cent or 
more of the total available area, there will be no significant effect except at high 
frequencies where the absorption might be reduced a little if the area of the holes 
is reduced. It depends on the spacing of the holes. The openings should not be 
spaced more than, say, half an inch or so apart. 

MR. WETHERELL: I cannot visualize whether that would be true. 

DR. COOK: Most people cannot. 

CHAIRMAN HARVEY FLETCHER: It works out that way mathematically. 

DR. COOK: I have an explanation. The sound wave comes up to a hole; the 
particles of air move faster as the sound goes through, and it then spreads out on 
the other side without appreciably reducing the amount getting through the hole. 
If you listen through a perforated screen, you can hear almost as well as when the 
screen is not present, which shows that the sound gets through without any 
difficulty. 

DR. LEO L. BERANEK: Some materials are designed to make use of those holes 
in reinforcing the absorption in a certain given frequency region. If the layer 
that is placed on the front of the material has a given thickness if it is not a really 
thin layer, which is what Dr. Cook was thinking of but if it has appreciable thick- 
ness, then the shape of that hole, the thickness and the diameter, may combine 
with properties of the material and the air space behind it to give an enhanced 
absorption at some frequency. That effect makes material like Celotex a good 
absorber in the region of 500 cycles per second. 

I wish to mention three kinds of materials touched on lightly or not mentioned 
at all. First let us consider a plywood surface. If one takes two sheets of ply- 
wood, either eighth-inch or quarter-inch, and bonds them loosely together by, 
say, spots of glue and places them in a room either in the form of curved sur- 
faces, or a flat layer spaced away from the wall, then you will find that you get 
quite large low-frequency absorption out of such a combination. We built a 
small studio recently at the Massachusetts Institute of Technology, and the rever- 
beration without the 'introduction of any absorptive material was around five 
tenths of a second, and fairly constant with frequency. 

CHAIRMAN FLETCHER: Without any absorption? 

DR. BERANEK: Except the plywood panels, and it was fairly constant up to 



1948 BEHAVIOR OF ACOUSTIC MATERIALS 201 

2000 cycles per second. Such panels generally become quite reflective above 1000 
cycles per second. You have to depend on the people in the room to provide the 
high-frequency absorption. So if you have cases where you want both diffusion 
of sound and you want absorption at low frequency, then these plywood sur- 
faces can be very effective. 

The rubberlike material which was mentioned, with an impervious facing on 
it, can absorb sound very effectively at low frequencies. At high frequencies it 
becomes reflective, and you have to depend on other means to provide absorption 
of sound. 

There are sound-absorbent cones and spheres but the cones are the only ones 
I have seen manufactured. They consist of a pair of cones back to back, hollow 
inside, made of half- or three-eighths-inch fiberboard of some kind. They are 
hung in the room. We have tried them and have had quite good results. My own 
opinion is that they are most useful in a room with a high ceiling, where if you 
put on the usual material, say inch-thick tile on the ceiling, you do not seem 
to get so much effect out of it. Sound bounces back and forth between the par- 
allel vertical walls, and by hanging these absorbers in the room, it is possible to 
get a great improvement in the acoustic results over those obtained by covering 
the ceiling only. Of course, they look peculiar. We put some up in some of the 
M.I.T. lecture rooms recently. We put them up in the Boston Art Museum and 
there was quite an article about "What Is New in Art Museums." 

MR. ZARO: Dr. Cook, in showing your slides, you showed the slides where 
you had brush-painted surfaces. What painting material did you use? Did you 
use a casein paint or a light mixture of linseed oil and oil paint? 

DR. COOK: The paint was an oil paint which was applied in such a way as to 
hide a black stripe painted on the surface. The application was not, shall I say, 
scientific. We wanted to get an idea of what might be expected from routine 
painting of the material. 

MR. ZARO: Would you care to project any recommendations as to the use of 
casein paint as against oil paint on such surfaces? 

DR. COOK: According to experiments made in our Sound Laboratory at the 
National Bureau of Standards, it seems that there is less tendency for a casein-type 
paint to fill up the holes of a porous material. It is quite safe sprayed on, but one 
must also be right after the painter to make sure he does not try to cover the fine 
holes due to porosity. 

MR. C. W. LUHRMANN: On the sprayed sample you had, was that sprayed 
asbestos or sprayed wool? I am familiar with sprayed asbestos and it loses very 
little sound absorption on painting. 

DR. COOK: Of the two slides I showed, neither referred to a sprayed-on or 
plastic-applied material. What you say is true. One still gets appreciable ab- 
sorption from some such materials after painting. 

MR. LUHRMANN: We recently put on a material of sprayed asbestos, and the 
architect was skeptical about paintability. He said, "I still think that it will not 
stand paint appreciably and still hold its sound absorption." So he requested that 
we paint that material as often as he desired, and we kept painting it, always 
using a spray coat until the paint began to drip off the ceiling. We had no equip- 
ment for absorption measurement there, but you could not detect any loss of 
sound absorption after the painting. 



202 COOK 

DR. COOK: I shquld not wish to comment on this unless I had seen the mate- 
rial. So much depends on the manner in which the material is applied, upon the 
density of application, and upon the painting. 

MEMBER: There is another commercial material on the market that does not 
seem to fit into the pictures that you had. It is called Kimsul, and consists of 
sheets of paper, held together very loosely, and it is faced with a sheet of loosely 
woven muslin. Is there some theory to explain its action? 

DR. COOK: I know the material you have in mind. That would probably come 
under the category of the rubberlike materials mentioned earlier. 

MR. E. J. CONTENT: Dr. Cook, do you think that you can apply any kind of 
paint on the surface of materials other than those that have perforations, and not 
change the absorption characteristics in any way as a function of frequency? 

DR. COOK: No, even for the rubberlike materials, repeated application of paint 
progressively reduces the absorption. 

MR. DUNBAR: Was the paint applied all at one time, or was it allowed to dry 
between coats? 

DR. COOK: The paint was allowed to dry a day or two between coats. 

MR. BEN SCHLANGER: Dr. Cook spoke about convex-faced material and 
said he was going to tell us more about it. 

DR. COOK: I was referring to spheres, cylinders, and cones. Yes, I did promise 
to say something about them. The sound can, so to speak, hit the material from 
all directions, whereas, when it is on a wall, the sound comes only from a hemi- 
sphere of directions. It appears that the greatest absorption obtains in the case of 
spheres, for a given material. 

MR. SCHLANGER: I do not favor materials that have to be painted, but during 
the war we could only get white acoustic materials, that is, factory-fabricated, 
and we did not want white. So what I did, instead of painting with a brush, was 
to use a dry-brush application, so there was no flow of material, and I continued 
to apply the dry-brush stipple effect, until sufficient coat-covering was achieved. 

MR. COLE: Dr. Cook, at what frequencies were the coefficients taken that you 
quoted with regard to the fissured material and the one following that? 

DR. COOK: Those were average coefficients, usually referred to as the noise 
coefficients. 





Continuously Variable Band 
Elimination Filter* 

BY KURT SINGER 

RCA VICTOR DIVISION, HOLLYWOOD, CALIFORNIA 



Summary A band-elimination filter continuously variable within a range 
from 30 to 9000 cycles has been developed. This device has proved ex- 
tremely useful for the elimination of interference frequencies in the produc- 
tion of sound for motion pictures. 

T THE REQUEST of one of the Hollywood motion picture studios, a 
continuously variable band-elimination filter has been developed 
which is capable of suppressing a very narrow frequency band any- 
where in the range from 30 to 9000 cycles. The immediate need for 
such a device was occasioned by the necessity to eliminate arc whis- 
tles from film recordings of one of the latest Technicolor productions. 
The arc whistles had been caused by commutator ripple modulation 
of the carbon arcs which were used for set illumination and had been 
picked up by the microphone. Because of the magnitude of the sets, 
such a great number of arc lights had to be employed that the series 
reactors, usually employed for arc-whistle suppression and which are 
connected between the motor-generator sets and the arc lights, became 
so badly overloaded that their attenuation was considerably reduced. 

The members of the Sound Department were aware of the problem, 
but since it was impossible to correct the condition at the time, they 
went ahead and recorded anyway, leaving the solution of the problem 
to be worked out during the re-recording, when various expedients 
could be tried. 

When the re-recording of the picture was started, tests with var- 
ious types of filters were made in an attempt to eliminate the arc 
whistles ; however, it was found that conventional filters did not cut 
sharply enough to permit elimination of the arc whistles without del- 
eterious effects on recording quality. Since the only solution was to 
eliminate the disturbing whistles electrically, we were asked whether 
it would be feasible to develop, on short order, a device suitable for 
the elimination of arc whistles in the neighborhood of 700 cycles. We 

* Presented October 24, 1947, at the SMPE Convention in New York. 

AUGUST, 1948 JOURNAL OF THE SMPE VOLUME 51 203 



204 SINGER August 

were also told "if we would be in a position to do not only this, but 
at the same time could elaborate on such a device and make it suitable 
for the elimination of deleterious noises anywhere in the audio spec- 
trum, then really we should be doing something for them and the 
film industry in general." 

The device which was finally developed to fulfill the studio's re- 
quirements is shown and explained in the accompanying illustrations. 
A zero-gain amplifier was used which consisted of four amplifier 
stages. A three-terminal adjustable Wien bridge was used as the 
coupling circuit between the second and third amplifier stages. 
Twenty-six decibels of feedback from output to input of the 
four stages narrows the bandwidth at cutoff frequencies. Fig. 1 
shows the input transformer, the secondary of which is terminated 
in a voltage divider which permits adjustment of the amplifier to zero 
gain. This transformer is connected into the grid of a pentode- 
connected 1620 tube which is resistance-coupled to another 1620 tube 
used as a triode. The plate of this second stage is fed back to the 
cathode of the first stage. This was primarily done to lower the im- 
pedance of the second 1620 tube sufficiently to present a very low 
generator impedance to the three-terminal Wien bridge which fol- 
lows. This expedient was necessary in order to prevent gain changes 
caused by impedance variations of the Wien bridge. It can be seen 
easily that as the generator impedance approaches zero, the genera- 
tor in this particular case is the plate impedance of the second stage, 
no gain change caused by impedance change of the Wien bridge will 
be experienced. Conversely, if the load impedance into which this 
Wien bridge works is very high as compared to the impedance of the 
Wien bridge itself, again no gain change will take place. 

Following this second stage is the Wien bridge which is a more or 
less standard three-terminal configuration. The audio spectrum 
from 30 to 9000 cycles is divided into five bands. This is accom- 
plished by changing the capacitance arms of the Wien bridge but 
keeping the variable range of the resistance arms the same for all five 
bands. By means of this arrangement, it is possible to cover ap- 
proximately a 3-to-l frequency range in the four bands from 60 to 
9000 cycles and slightly better than a 2-to-l range from 30 to 68 
cycles. The output of this Wien bridge is fed into the grid of another 
1620 tube, pentode-connected, which in turn is resistance-coupled to 
a triode-connected 1620. The plate of this fourth stage is connected 
to a suitable output transformer and a portion of the output voltage 



VARIABLE BAND-ELIMINATION FILTER 



205 




206 



SINGER 



August 



ATTENUATION CHARACTERISTIC 
OF WIEN BRIDGE 

NO FEEDBACK 
500-500,000 n 



000 
FREQUENCY IN CYCLES PER SECOND 




10,000 20. Ob 



Fig. 2 



is fed back, 180 degrees out of phase, to the cathode of the first stage. 
This over-all feedback results, first, in a considerable decrease of 
over-all amplifier distortion. Second, since it corrects for frequency- 
response variations within its limitations, it narrows the bandwidth 
of the band which is eliminated at the cutoff frequencies. 



i 






i 

LJ 

- 


10 
20 
30 
40 
50 

t 














NUATION CHARACTERISE 
OF WIEN BRIDGE 
26DB FEEDBACK 
500-500,000 fl 






















" ATTE 














































































































1* 










































































































































































































































































































































































































































































































































1 , ... 


































1 













100 










1000 








10,00 


20, 



FREQUENCY IN CYCLES PER SECOND 



Fig. 3 



1948 VARIABLE BAND-ELIMINATION FILTER 207 

Figs. 2 and 3 give a better picture of what is meant by narrowing 
the bandwidth. Normally, a Wien bridge when used between two 
amplifier stages attenuates rather gradually and the slope becomes 
progressively steeper. With the use of over-all feedback around the 
Wien bridge, the biggest part of this gradual region is eliminated and 
the sides of the eliminated band are made considerably steeper. 
Two variable, vernier resistors in the Wien bridge permit obtaining 
an exact null. Fig. 4 shows a front view of the filter panel. The 
large center dial permits selection of any frequency within the specific 
band which is selected by setting of the rotary switch directly below. 
The two smaller dials to the left and right of this large dial are the 
two verniers, which assist in obtaining an accurate null. There is 




Fig. 4 Front view. 

an "on-and-off" switch to the right and an "in-and-out" switch to 
the left. This "in-and-out" switch permits removal or insertion of 
this filter in the recording line at the operator's discretion. No click 
or other disturbance is created when this filter is switched in and out 
of the circuit. 

Fig. 5 shows the interior of the device and Fig. 6 shows the fre- 
quency characteristics as obtained with various settings of the dip- 
I control dials. The bandwidth of the rejected frequency band is 
; approximately 15 per cent at 6 decibels attenuation and 3 per cent at 
' 30 decibels attenuation as referred to the peak-attenuation frequency. 
The practical operation of the filter takes place in the following 
| manner. Usually, one determines the exact frequency of the inter- 
I ference by beating it with an oscillator. Then the band-elimination 



208 



SINGER 



August 



filter is connected into the recording circuit and the same frequency 
as the interference is injected into the recording channel directly from 
the oscillator. The frequency derived from the oscillator is elimi- 
nated by means of the proper dial adjustments on the filter. This is 
first done by ear and the ultimate and lowest setting is obtained by 
means of high-gain volume indicators. The minimum attenuation of 
the interference frequency which can thus be obtained is 50 decibels. 
After the proper setting of the filter has been determined, the oscil- 
lator is disconnected and the recording channel repatched for normal 
operation with the band-elimination filter in the circuit. If the in- 




Fig. 5 Chassis view. 

terferences consisted of a single frequency only, this frequency has 
been eliminated. However, if there were higher-order harmonics 
present they, of course, have been retained. How objectionable j 
these harmonics are, depends upon their magnitude. In the case of; 
the previously mentioned arc whistles, it was possible to eliminate them 
completely by the use of this filter just by eliminating the fundamental. 
It has also been found possible to find further use for this filter byj 
using it for the elimination of camera noise and motor-generator 
noise. Some added explanation might be in order. Camera noise, 
is, as the name implies, generated by the motion picture camera.] 
Most studios use blimps, that is, soundproof housings over the cameraj 



1948 



VARIABLE BAND-ELIMINATION FILTER 



209 



which are supposed to remove camera noise completely. Some 
blimps, however, are not so good as others and under certain condi- 
tions it is impossible to use blimps. Then one has to rely on low- 
noise cameras which are not always low noise, the noise being a func- 
tion of maintenance and wear. While camera noise does not consist 
of only a single frequency, it has been found possible to reduce its 
objectionable effects almost completely by the use of this filter 
by eliminating the predominating noise frequency. 

Motor-generator sets used for lighting current on location are 
usually quite noisy since they employ gasoline motors. While an 
attempt is usually made to keep them as far from the microphone as 



TYPICAL ATTENUATION 

CHARACTERISTICS OF 

Ml 10135 VARIABLE BAND 

ELIMINATION FILTER 




FREQUENCY IN CYCLES PER SECOND 



Fig. 6 

possible, there are practical limitations to this distance, with the re- 
sult that some studios have motor-generator-noise interference on a 
number of their location shots. There again it has been found that 
the elimination of the predominating noise frequency is sufficient to 
attenuate the generator noise satisfactorily. 

In conclusion, the summary of the electrical characteristics of this 
band-elimination filter are as follows: The gain of the filter is zero 
decibels, the input impedance is 600 or 250 ohms, and the output 
impedance is 600 or 250 ohms. Zero gain is maintained whether the 
250- or 600-ohm input or output connections are used. The filter 
operates from a heater supply of 6 to 12 volts direct current and B 
supply of 250 volts direct current. Four RCA 1620 Radiotrons are 



210 SINGER 

employed. The maximum input level that can be applied is 2 
dbm.* The distortion at an input or, for that matter, output 
level of 2 dbm without the frequency-selective circuit, is about 
0.15 per cent from 50 to 8000 cycles. With the frequency-selective 
bridge in the circuit, it is somewhat difficult to express distortion in 
terms of percentage of fundamental frequency, if the fundamental 
frequency lies in the attenuation band, since the ratio of fundamental 
to harmonic is determined primarily by the attenuation of the funda- 
mental frequency. However, for fundamentals which are outside 
the attenuation band, the distortion is not any more than 0.15 per 
cent. The peak rejection frequency is continuously adjustable be- 
tween 30 and 9000 cycles. At least 50 decibels rejection is obtained 
at any peak rejection frequency. The frequency spectrum from 20 
to 9000 cycles is divided into five overlapping bands. A sixth posi- 
tion on the selector switch permits removal of the frequency-selec- 
tive Wien bridge so that the device may be operated as a flat zero-gain 
amplifier which sometimes is useful if one wants an isolation amplifier. 
The mechanical construction of this filter, which is known as the 
MI-10135, permits mounting in a standard relay rack. The front 
panel dimension is 19 X 10V 2 inches. All tubes are nonmicrophoni- 
cally mounted and the frequency-selective Wien bridge, as well as the 
entire wiring, are completely shielded against electrostatic and elec- 
tromagnetic fields. A dust cover, which is removable from the rear, 
is also provided. 

* Decibels with respect to 0.001 watt. 

DISCUSSION 

MK. GEORGE LEWIN: Is there any noticeable effect whatever on the quality of 
voice or music with this filter in operation? 

MR. E. E. MILLER: I do not believe the effect on voice or music through the 
insertion of this filter is any more than that you will notice in a studio on the 
scoring stage where you move the microphone an inch and a half wavelength at any 
particular frequency to pick up the peak or null of a standing wave that exists 
in that studio. I do not believe you will find this is any more than that. 

DR. HOWARD C. HARDY: . I do not have so much enthusiasm as the speaker had 
for the fact that you could take out the noise of a motor generator or camera by 
this filter; certainly the spectra of some of those instruments are very wide 
bands, and no peak usually exists that is over 60 or 70 decibels above the whole 
main spectrum. At the most, you could eliminate 60. 

MR. MILLER: I think the author makes that very clear. He pointed out that 
if a high order of harmonics exists, we can remove the fundamental but not the 
harmonic if it is of a high order. 



Society Announcements 



Czechoslovak Film Standards 

As of July 1, 1948, the standard projection speed for 35-mm sound film in 
Czechoslovakia will be 25 frames per second rather than the American Standard 
of 24 frames per second. Mr. Frantisek Pilat, president of the Filmovy Technicky 
Sbor (Czechoslovak Motion Picture Engineering Committee), reports that this 
change was made because of the increased use of synchronous motors in theater 
projectors in that country and also because of the 50-cycle power-line frequency 
that is in common use in most European countries. With synchronous drive, 
speed-regulation problems cease to exist as long as the line frequency is constant, 
and, according to Mr. Pilat, practical tests proved that the resulting higher pitch 
of the reproduced sound created no practical problems since it was not observed 
by spectators. 

International Scientific Film Congress 

The second congress of The International Scientific Film Association will be 
held in London from October 4 to 11, 1948. 

The Association was constituted last year in Paris by delegates from 22 coun- 
tries who had accepted the joint invitation to the inaugural congress from The 
Scientific Film Associations of Great Britain and France. The primary aim of 
the Association is: 

"To raise the standard and to promote the use of the scientific film and related 
material throughout the world in order to achieve the widest possible under- 
standing and appreciation of scientific method and outlook, especially in 
relation to social progress." 

This year's congress is being convened by The Scientific Film Association of 
Great Britain, with the help of The British Film Institute, and invitations have 
already been issued to countries throughout the world. The congress will open 
with a formal reception to the delegates on October 4 and the following three 
days will be devoted to business meetings of The International Scientific Film 
Association. On October 8, 9, and 10 there will be a Festival of Scientific Film 
when it is hoped to show many contributions from all the participating countries 
to members of the general public. The congress will close with a general assembly 
of the delegates on October 11. 

The .widespread public interest in England in the scientific film as evidenced 
by over 10,000 members of local scientific film societies, the introduction of 
scientific films and other visual aids into the educational program in that country 
and, in particular, the many pioneer activities of The Scientific Film Association 
with its country-wide membership make it particularly appropriate that this 
congress should be held in Great Britain. Visitors from overseas will have an 
opportunity of studying the many contributions which England has made by 
the use of films to the "widest possible understanding and appreciation of scien- 
tific method and outlook." 

Further details may be obtained from The Scientific Film Association of 
34 Soho Square, London, W.I. 

211 



64th Semiannual Convention 

Hotel Statler, Washington, D. C., October a5-29, 1948 



-PAPERS PROGRAM 

Preparations are being made for the Fall Meeting of the Society which will be 
held at the Statler Hotel in Washington, D. C., October 25 to 29, 1948, inclusive. 
Authors desiring to submit papers for presentation at this meeting are requested 
to obtain Author's Forms from the Vice-Chairman of the Papers Committee 
nearest them. The following are the names and addresses: 

Joseph E. Aiken E. S. Seeley N. L. Simmons 

225 Orange St., S. E. 250 West 57 Street 6706 Santa Monica Blvd. 

Washington 20, D. C. New York 19, N. Y. Hollywood 38, Calif. 

R. T. Van Niman H. L. Walker 

4431 West Lake St. P. O. Drawer 279 

Chicago 24, Illinois Montreal 3, Que., Canada 

Author's Forms and summaries of papers must be in the hands of Mr. Aiken 
by September 1. 

-PRELIMINARY CONVENTION PROGRAM 

Present plans for the 64th Convention Program include a number of special 
features that will be of interest to all Society members. There will be a sym- 
posium on High-Speed Photography now being organized by Mir. J. H. Waddell, 
Chairman of the SMPE Committee on High-Speed Photography, and it is ex- 
pected that a large group of interesting and related papers on the subject will be 
presented. 

BUSINESS SESSION 

The annual Society Business Meeting is scheduled for 3:00 P.M., Tuesday, 
October 26. All members planning to be in Washington should attend this ses- 
sion since there will be important items of business to be discussed and voted upon . 

-AWARDS 

Annual presentation of Society awards is planned and recipients are now being 
determined by the SMPE Committees on Journal Awards, Fellow Awards, 
Samuel L. Warner Memorial Award, and Progress Medal Award. Also, the 
newly elected Society officers will be introduced to the members. 
212 



PRELIMINARY PROGRAM 



Monday, October 25, 1948 
9 : 30 A.M. REGISTRATION. 

Capitol Terrace Room 
12:30 P.M. GET-TOGETHER LUNCHEON 

Congressional Room 
3:00 P.M. TECHNICAL SESSION 

Presidential Ballroom 
8:00 P.M. TECHNICAL SESSION 

Presidential Ballroom 

Tuesday, October 26, 1948 
9 : 30 A.M. REGISTRATION 

Capitol Terrace Room 
10 : 00 A.M. TECHNICAL SESSION 

Presidential Ballroom 
2:00 P.M. TECHNICAL SESSION 

Presidential Ballroom 
3:00 P.M. BUSINESS SESSION OF THE 

SOCIETY 

Presidential Ballroom 
3: 30 P.M. RESUMPTION OF TECH- 
NICAL SESSION 
Presidential Ballroom 
OPEN EVENING 



Wednesday, October 27, 1948 
9 : 30 A.M. REGISTRATION 

Capitol Terrace Room 
10: 00 A.M. TECHNICAL SESSION 

Presidential Ballroom 
OPEN AFTERNOON 
8: 30 P.M. 64TH SEMIANNUAL BAN 

QUET 
Presidential Ballroom 

Thursday, October 28, 1948 

OPEN MORNING 
2:00 P.M. TECHNICAL SESSION 

Presidential Ballroom 
8:00 P.M. TECHNICAL SESSION 

Location to be an- 
nounced later 

Friday, October 29, 1948 

10: 00 A.M. TECHNICAL SESSION 

Presidential Ballroom 
2 : 00 P. M. TECHNI CAL SESSI ON 

Presidential Ballroom 
5:00 P.M. ADJOURNMENT 



-LADIES' ACTIVITIES 

The Ladies' Reception Hostess and Mr. W. C. Kunzmann are arranging a most 
interesting program for ladies who plan to attend the Convention or to visit 
Washington during Convention week. The Potomac Room at the hotel will be 
ladies' headquarters; further information about the special program will appear in 
the September issue of the JOURNAL. 



-RESERVATIONS 

Excellent accommodations at the Hotel Statler have been arranged for by the 
Convention Committee. Members of the Society will receive reservation cards, 
which they will be requested to fill out and mail directly to the hotel in Washing- 
ton. Each member must arrange these accommodations directly with the hotel; 
be sure to mention the SMPE Convention if you are writing on your own letter- 
head. Reservations should be made by September 15. 



213 



Book Reviews 



Magic Shadows, by Martin Quigley, Jr. 

Published (1948) by the Georgetown University Press, Washington, D. C. 161 
pages + 14-page appendix + 8-page bibliography + 7-page index. 24 illustra- 
tions. GVsXOVa inches. Price, $3.50. 

Film historians, recording the origins of the motion picture, seem impelled to 
begin their studies with the Altamira cave paintings and then, working up slowly 
through Leonardo, Rog6t, and Plateau, they finally come to Muybridge, Marey, 
and the Edison prescreen experiments. Actually, the relationship of their 
historic discoveries and devices to the history of the film itself is more than a 
little remote; Mr. Quigley has quite properly removed this chapter from the 
film histories and expanded it into a book that has its own validity. "Magic 
Shadows" carefully traces the slow accretion of scientific knowledge, the sudden 
acceleration in the mid-nineteenth century as early principles found practical 
application, and finally the simultaneous rush to the screen in France, England, 
Germany, and the United States in 1895-1896. Through it all Mr. Quigley 
stresses the internationality of the sources, the innumerable individuals who 
contributed to the scientific study of optics, and the universal appeal, not merely 
of films today, but of the more basic urge to project the shadow of reality. An 
elaborate chronology at once traces the growth of prescreen knowledge and em- 
phasizes this multiplicity of its sources. 

That same multiplicity is further revealed in the extensive bibliography that 
Mr. Quigley has appended to his book. Working intermittently on it since 1936, 
he has had opportunity to examine original sources both here and abroad, has 
covered printed material in Latin, French, German, and English, and translations 
from Greek and Arabian. But "Magic Shadows" is no mere compilation. The 
main lines of the study were laid down by the veteran film historian, Terry 
Ramsaye. In following them, Mr. Quigley has produced a study that is as 
readable as it is useful, as thoughtful as it is informative. 

JOHN E. ABBOTT 

Webb and Knapp, Inc. 

New York 17, N. Y. 

Photographic Facts and Formulas, by E. J. Wall and Franklin I. 
Jordan 

Published (1947) by the American Photographic Publishing Company, 353 
Newbury St., Boston 15, "Mass. 353 pages + 10-page index + vii pages. 18 
illustrations. &/ 4 X 9Y 4 inches. Price, $5.00. 

This book is literally crammed with a multitude of both facts and formulas. 
The new revision represents a minor modernization of the 1940 edition to include 
references to recent developments such as coated lenses and the new color processes. 
The material for the most part is presented in a clear and readable fashion with a 
continuity of subject matter that was not evident in the 1924 and earlier editions. 
The publisher's claim, however, that it is a practical handbook of directions for all 
214 






Book Reviews 



photographic operations in common use is not strictly valid. The increasingly 
important field of color photography, for example, is glossed over in twenty pages, 
less than half the space allotted this subject in the 1940 edition. On the other 
hand, the preparation of lantern slides, which is currently something of a lost 
art, is allotted sixteen pages, and a process as obsolete as the making and toning 
of printing-out papers is treated in exquisite detail. 

Black-and-white photography is quite fully and capable handled, and the 
experimental photographic hobbyist will be delighted at the practical working 
approach to such subjects as image toning; the sensitizing of leather, fabrics, 
and wood; oil, bromoil, and other transfer processes; gum-bichromate printing; 
and carbon processes. There is a tendency, particularly in the chapter on "Photo- 
mechanical Processes," to pile up formulas and working directions without any 
real description of the process involved. In general, the material appears to have 
been drawn from a variety of sources without too careful an effort to unify it. 

Such important fields as reversal processing and tropical processing are only 
sketchily treated, and there is a regrettable tendency to retain obsolete terminol- 
ogy in some of the older formulas such as boracic acid and carbonate of soda. 

Despite these objections, the book is a sufficiently useful compendium of photo- 
graphic information to be a worthy adjunct to the photographer's library. How- 
ever, full-scale revision rather than mere deletion and addition is overdue. In 
view of the enormous amount of pertinent photographic material available to the 
compilers, there is not space in a photographic handbook of modest size for an 
entry on "How to Make Marine Glue" or for five pages on "How to Resilver 
Mirrors." 

HOWARD A. MILLER 

Eastman Kodak Company 

Kodak Park, Rochester, N. Y. 




FORTY YEARS AGO 

Political Subjects Desired 

A correspondent of the "St. Louis Post-Dispatch" says: "I should 
like to ask through your columns why the moving picture show com- 
panies do not make arrangements for a reproduction of the proceedings 
of the Republican and Democratic national conventions that are to be 
held soon? It would be very interesting and instructive, and millions 
who are unable to go to the convention halls would like very much to 
see it. And other notable gatherings should be reproduced." 

The Moving Picture World, June 18, 1908 

215 



Section Meeting 



Midwest 

George W. Colburn, secretary-treasurer of the Midwest Section, presided at the 
May 13, 1948, meeting, which was held on the sound stage of the Atlas Film Cor- 
poration. Ninety-two members and guests were present. 

The first paper, "The DM-2 and DM-4 Developing Machine," was presented 
informally by R. Paul Ireland, president, Engineering Development Laboratories. 
Mr. Ireland described the physical setup of the machines and elucidated on the 
features of roller design and the principles of physics involved. 

"The RCA Six-Position Re-Recording Console" by Everett Miller of the 
Radio Corporation of America was read by Frank Richter, sound engineer. 
Atlas Film Corporation. The installation described by the paper was inspected 
after the final presentation. 

Erik I. Nielsen, senior organic chemist, Armour Research Foundation, gave a 
talk entitled "Recent Developments in Plastics." This subject dealt with plastics 
as applied to optics anol covered the problems involved hi mass production of high 
quality plastic lenses. 

The meeting adjourned at 10:00 P.M. and was followed by an inspection of the 
developing machines described in the first presentation, the re-recording console 
described in the second paper, and a general tour of the Atlas Film Corporation's 
facilities. 



Correspondence 



It is highly desirable that members avail themselves of the opportunity 
to express their opinions in the form of Letters to the Editor. When of 
general interest, these will be published in the JOURNAL of the Society of 
Motion Picture Engineers. These letters may be on technical or non- 
technical subjects, and are understood to be the opinions of the writers and 
do not necessarily reflect the point of view of the Society. Such letters 
should be typewritten, double-spaced. If illustrations accompany these 
contributions, they should be drawings on white paper or blue linen and 
the lettering neatly done in black ink. Photographs should be sharp 
and clear glossy prints. 

Please address your communications to 

Miss HELEN M. STOTE, Editor 

Society of Motion Picture Engineers 

Suite 912 

342 Madison Avenue 

New York 17, N. Y. 



216 






Current Literature 



THE EDITORS present for convenient reference a list of articles dealing with 
subjects cognate to motion picture engineering published in a number of se- 
lected journals. Photostatic or microfilm copies of articles in magazines that are 
available may be obtained from The Library of Congress, Washington, D. C., or 
from the New York Public Library, New York, N. Y., at prevailing rates. 



American Cinematographer 
29, 4, April, 1948 
Television Field Opens for Cinema- 

tographers (p. 120) E. Tow 
Progress on 8-mm Synchronized 
Sound (p. 135) 

29, 5, May, 1948 
Extremely Wide Angle Lens for 

Aerial Mapping (p. 154) 
Appreciating the Motion Picture 
(p. 163) C. LORING 

International Projectionist 
23, 4, April, 1948 

Theater Television: A General 
Analysis (p. 21) A. N. GOLDSMITH 

More on "Quality" vs. "Pleasing" 
Sound Reproduction (p. 30) 
23, 5, May, 1948 

Optical Efficiency in Projection (p. 5) 
R. A. MITCHELL 

Screen Data: Types, Sizes, Illumi- 
nation for 35- and 16-mm Film 
Projection (p. 8) 

Handling, Storing Cine Film (p. 12) 

Theater Television: A General 
Analysis (p. 15) A. N. GOLDSMITH 

Tele-Tech 

7, 6, June, 1948 

Sound Measurements in BC Studios 
(p. 38) W. JACK 



Audio Engineering 

32, 5, May, 1948 

Loudness Control for Reproducing 
Systems (p. 11) D. C. BOMBERGER 
Factors Affecting Frequency Re- 
sponse and Distortion in Magnetic 
Recording (p. 18) J. S. BOYERS 
Horn-Type Loudspeakers (p. 25} 

S. J. WHITE 
British Kinematography 

12, 4, April, 1948 

Metals hi Kinema and Related 
Equipment (p. 109) A. B. EVEREST 
and F. HUDSON 

Back Projection and Perspective. 
1. Interlocking and Film Steadi- 
ness (p. 127) G. HILL 
La technique cinematographique 

19, April 1, 1948 

Trente annees de technicolor. 
(Thirty Years of Technicolor) 

(p. 133) W. R. GREENE 
Precedes d'enregistrement sonore sur 
film. (Procedure of Recording 
Sound on Film) (p. 135) 
P. JACQUIN 
Radio News 

39, 6, June, 1948 
The Recording and Reproduction of 

Sound. Pt. 16 (p. 65) O. READ 
Modern Television Receivers. Pt. 3 
(p. 71) M. S. KIVER 



EMPLOYMENT SERVICE 
POSITION WANTED 

CAMERAMAN: Experienced in 35-mm and 16-mm cinematog- 
raphy, color, black-and-white. Active member SMPE. Three 
years' overseas experience as Official Army Photographer World 
War II. Will consider offer anywhere in U.S.A. References 
available. Free to travel part time at least. Write Charles Arnold, 
P. O. Box 995, Peoria, 111. 



217 



New Products 



Further information concerning the material described below can 
be obtained by writing direct to the manufacturers. As in the case 
of technical papers, publication of these news items does not consti- 
tute endorsement of the manufacturer's statements nor of his products. 



Synchro-Link, Pulsing Drive, 
and Dyna-Link 

Yardeny Laboratories, 105-107 

Chambers Street, New York 7, New 
York, recently put on the market their 
Synchro-Link, Pulsing Drive, and 
Dyna-Link. 

The Synchro-Link is an inexpensive 
remote-positioning servo control, which 
will position one or several distant 
motors, according to the setting of the 
master-control dial. The accuracy is 
independent of the load. 




This equipment works on the prin- 
ciple of a self-balancing electronic 
bridge, and will control the speed ad- 
justment on variable-speed transmis- 
sions, the setting of motorized valves, 
volume dampers, engine throttles, 
pumps, machine tools, and special 
machinery. 

The master-control dial can be lo- 
cated any distance from the Synchro- 
Link controller up to several thousand 
feet. Only 3 wires of light gauge pass- 
"ing small control currents connect the 
master control to the Synchro-Link 
controller. 

218 



The Pulsing Drive is a new device for 
controlling electrical motors when ac- 
curate positioning is important. It 
responds to the operation of a single 
knob, and when this knob is rotated in 
one direction, the Pulsing Drive closes 
selectively one of two circuits for very 
short periods of time repeated at a rate 
dependent upon the speed of the knob 
rotation. It is suited for controlling all 
standard types of electric motors or 
magnetic valves. 

The Dyna-Link is an electronic con- 
trol device, designed for industrial 
applications of variable-speed power 
transmission. It consists of a master 
control calibrated in revolutions per 
minute, the Dyna-Link controller, and 
a speed-measuring generator. When 
the operator sets the master control to 
the desired speed setting, the Dyna- 
Link controller energizes the pilot 
motor in the proper direction for ad- 
justing the speed changer until the 
actual output speed corresponds to the 
master-control setting. If the drive 
slows down because of an increase hi 
the load, the Dyna-Link controller 
automatically detects the difference in 
speed and corrects the adjustment. 

Film Counter, Audio Compensa- 
tor, and Phase Converter 

A Film Counter, Audio Compensa- 
tor, and Phase Converter are three 
new products which are now being 
produced by Arlington Electric Prod- 
ucts, 500 W. 25 St., New York, Ne\v 
York. 



New Products 



Further information concerning the material described below can 
be obtained by writing direct to the manufacturers. As in the case 
of technical papers, publication of these news items does not consti- 
tute endorsement of the manufacturer's statements nor of his products. 



The Film Counter is designed for 
use in motion picture viewing, dubbing, 
recording, and narrating, wherever 
footage and cuing information are 
desired. 

The unit can be located remotely 
from a projector, recorder, or dubbing 
head and will read elapsed time in 
minutes and tenths of a minute and in 
feet of film that have passed through 
the film machine. The counter can be 
wired to start automatically with the 
projector or dubbing head and can be 
stopped and started any number of 
tunes during a thousand-foot reel. 




The Audio Compensator is used 
j where audio equalization is required, 
! and is applicable in film recording, disk 
I recording, and general broadcast-studio 



work. Equalization characteristics 
available consist of three steps each 
lowering or raising low frequencies 
and lowering or raising high frequen- 
cies. Each channel contains a two- 
stage resistance-capacitance amplifier 
employing Type 1620 tubes ; Power 
and audio connections are made 
through multiple plugs. 

The Phase Converter is designed for 
use where it is necessary to operate 
cameras or recording machines with 
three-phase driving motors from a 
single-phase source of power. 

The converter is portable and does 
not use electronic tubes or rotating 
machinery. The converter input is 
115-volt, 60-cycle, single-phase alter- 
nating current, and the output is 220- 
volt, 60-cycle, three-phase alternating 
current of sufficient power to run one 
motor properly. A motor running 
from this converter will have the elec- 
trical characteristics identical to that 
of commercial three-phase power and 
will have a speed synchronous to the 
single-phase line frequency. 



FORTY YEARS AGO 

Washington, D. C., Wants Picture Machines Inclosed 

Fire Chief Belt has recommended to the Commissioners that moving 
picture machines used in the five-cent theaters and the regular theaters 
of the District be inclosed in fire-proof boxes. 

The Moving Picture World, May 9, 1908 

219 



SECTION OFFICERS 

Atlantic Coast 

Chairman Secretary-Treasurer 

William H. Rivers Edward Schmidt 

Eastman Kodak Co. E. I. du Pont de Nemours & Co. 

342 Madison Ave. 350 Fifth Ave. 

New York 17, N. Y. New York 1, N. Y. 



Midwest 

Chairman Secretary-Treasurer 

R. T. Van Niman George W. Colburn 

Motiograph George W. Colburn Laboratory 

4431 W. Lake St. 164 N. Wacker Dr. 

Chicago 24, 111. Chicago 6, 111. 



Pacific Coast 

Chairman Secretary-Treasurer 

S. P. Solow G. R. Crane 

Consolidated Film Industries 21224 St. 

959 Seward St. Santa Monica, Calif. 
Hollywood, Calif. 

Student Chapter 
University of Southern Calfornia 

Chairman Secretary -Treasurer 

Thomas Gavey John Barnwell 

1046 N. Ridgewood PI. University of Southern California 

Hollywood 38, Calif. Los Angeles, Calif. 



Office Staff New York 

EXECUTIVE SECRETARY OFFICE MANAGER 

Boyce Nemec Sigmund M. Muskat 

STAFF ENGINEER JOURNAL EDITOR 

Thomas F. Lo Giudice Helen M. Stote 



Cecelia Blaha Dorothy Johnson 

Helen Goodwyn Ethel Lewis 

Beatrice Melican 



220 



Journal of the 

Society of Motion Picture Engineers 



VOLUME 51 



SEPTEMBER 1948 



NUMBER 3 



PAGE 

Report of the President LOREN L. RYDER 221 

Historical Sketch of Television's Progress L. R. LANKES 223 

Report of SMPE Standards Committee 230 

Errors in Calibration of the / Number. . . .FRANCIS E. WASHER 242 

Projection Equipment for Screening Rooms H. J. BENHAM 261 

The Gaumont-Kalee Model 21 Projector 

L. AUDIGER AND R. ROBERTSON 269 

Zoomar Lens for 35-Mm Film F. G. BACK 294 

Parabolic Sound Concentrators R. C. COILE 298 

Committees of the Society 312 

64th Semiannual Convention : 323 

Section Meeting 327 

Book Review: 
"The Preparation and Use of Visual Aids/' by Kenneth B. 

Haas and Harry G. Packer 

Reviewed by W. A. Wittich 330 



ARTHUR C. DOWNBS 

Chairman 
Board of Editors 



HELEN M. STOTE 
Editor 



GORDON A. CHAMBERS 

Chairman 
Papers Committee 



Subscription to nonmembers, $10.00 per annum; to members, $6.25 per annum, included in 
their annual membership dues; single copies, $1.25. Order from the Society's general office. 
A discount of ten per cent is allowed to accredited agencies on orders for subscriptions and 
single copies. Published monthly at Easton, Pa., by the Society of Motion Picture Engineers, 
Inc. Publication Office, 20th & Northampton Sts., Easton, Pa. General and Editorial Office, 
<J42 Madison Ave., New York 17, N. Y. Entered as second-class matter January 15, 1930, 
at the Post Office at Easton, Pa., under the Act of March 3, 1879. 

Copyright, 1948, by the Society of Motion Picture Engineers, Inc. Permission to republish 
material from the JOURNAL must be obtained in writing from the General Office of the Society, 
t/opyright under International Copyright Convention and Pan-American Convention. The 
Society is not responsible for statements of authors or contributors. 



Society of 

Motion Picture Engineers 

342 MADISON AVENUE NEW YORK 17, N. Y. TEL. Mu 2-2185 
BOYCE NEMEC . . . EXECUTIVE SECRETARY 

OFFICERS 

1947-1948 

PRESIDENT EDITORIAL VICE-PRESIDENT 
Loren L. Ryder Clyde R. Keith 

5451 Marathon St. 233 Broadway 

Hollywood 38, Calif. New York 7, N. Y. 

PAST-PRESIDENT CONVENTION VICE-PRESIDENT 
Donald E. Hyndman William C. Kunzmann 

342 Madison Ave. Box 6087 

New York 17, N. Y. Cleveland, Ohio 

EXECUTIVE VICE-PRESIDENT SECRETARY 
Earl I. Sponable G. T. Lorance 

460 West 54 St. 63 Bedford Rd. 

New York 19, N. Y. Pleasantville, N. Y. 

1948-1949 

ENGINEERING VICE-PRESIDENT FINANCIAL VICE-PRESIDENT 

John A. Maurer James Frank, Jr. 

37-0131 St. 18 Cameron PI. 

Long Island City 1, N. Y. New Rochelle, N. Y. 

TREASURER 

Ralph B. Austrian 
247 Park Ave. 
New York 17, N. Y. 

Governors 

1947-1948 

John W. Boyle Robert M. Corbin Charles R. Daily 

1207 N. Mansfield Ave. 343 State St. 5451 Marathon St. 

Hollywood 38, Calif. Rochester 4, N. Y. Hollywood 38, Calif. 

David B. Joy Hollis W. Moyse 

30 E. 42 St. 6656 Santa Monica Blvd. 

New York 17, N. Y. Hollywood, Calif. 

1948 

William H. Rivers S. P. Solow R. T. Van Niman 

342 Madison Ave. 959 Seward St. 4431 W. Lake St. 

New York 17, N. Y. " Hollywood, Calif. Chicago, 111. 

1948-1949 

Alan W. Cook Gordon E. Sawyer 

4 Druid PI. Lloyd T. Goldsmith 857 N. Martel St. 

Binghampton, N. Y. Burbank, Calif. Hollywood, Calif. 

Paul J. Larsen 

Los Alamos Laboratory 
University of California 
Albuquerque, N. M. 



Report of the President 



THIS REPORT of the President is the story of the Society of Motion 
Picture Engineers, its activities during the last six months, and 
\vhat takes place at the New York Headquarters' Office 3000 miles 
from this, the 63rd Semiannual Convention. 

I am proud of that "63rd" figure and the continuity of activity 
which it represents. Few people realize that for 31 1 / 2 years this 
Society has served this industry. Few people realize that much of 
the early world- wide standardization for silent pictures was worked 
out by SMPE members. As of this date this industry has estab- 
lished more standards with the American Standards Association than 
any other United States industry. This is important, for our market 
is world-wide and dependent upon the existence and the retention of 
standards under which our product can be played. The Society is 
still active and a look into the future would indicate that television 
will bring more and greater problems in standardization. It is im- 
portant to note that the economic value of this standardization in- 
creases rapidly with complexity of equipment, and even to one famil- 
iar with television it is complex. 

The 62nd Convention of the Society, which was held in New York 
last October, included a Theater Engineering Conference and Equip- 
ment Exhibit. It brought into our circle many theater people and 
their technical contributions along with an appreciation on our part 
of their problems. The good which has resulted from that conven- 
tion will be of lasting value. 

The period following the New York Convention has been marked 
by great technical changes. Television has grown from the ten-inch 
image of a home receiver to a reality on the theater screen. This is a 
milestone in motion pictures. It may bring about even greater 
changes than occurred with the advent of sound. 

Our progress has not been limited to any one field. New color 
processes are now in commercial use and the thinking which has taken 
place is the forerunner to the great program of color papers at the 
63rd Convention. The completeness of this color coverage is not an 
accident. It is the result of a realization on the part of our engineers 
that color offers an outstanding technical advantage which the motion 

* Presented May 17, 1948, at the SMPE Convention in Santa Monica. 

SEPTEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 221 



222 RYDER 

picture industry has and can use in meeting the competition of tele- 
vision broadcasting to the home. 

Magnetic recording has arrived at a state of development where it 
is now finding its place as a tool for the broadcast and motion picture 
industries. The papers presented at this convention and the work 
of our Standards Committee will aid in the best use of this note- 
worthy scientific development. There are other fields in which 
there has been marked advancement and I say with pride that these 
advancements are well recorded in the JOURNAL of the Society. 

Over the years the Society has progressively and solidly grown into 
a large and businesslike organization. Our Headquarters' Offices are 
located in the Canadian Pacific Building at 342 Madison Avenue, 
New York 17, New York. We have a paid staff of eight persons 
under Mr. Boyce Nemec, the Executive Secretary. The work which 
they do is the background of all Society activity world-wide. Our 
sections are located in New York, Chicago, and Hollywood, with a 
Student Chapter at the University of Southern California. All of our 
membership records, business administration, and the publication of 
our JOURNAL are handled by the New York Office. The New York 
Office and the personnel in that office are there to serve you, the 
members of this Society. Please visit the office when you are in 
New York or write whenever we can be of assistance to you. 

The records as of March 31, 1948, show that our membership has 
now reached 2787 members. For the year 1948 we anticipate a 
revenue and an expenditure of approximately $95,000. 

In making a study of our membership we find that it has not grown 
as anticipated. This seems to be largely due to the complexity of 
the system of admitting new members. Steps have been taken at 
the Board Meeting of May 16 to rectify this condition. All persons 
interested in the art of motion picture making are eligible for Asso- 
ciate membership. We want their affiliation and we want to advance 
their status when, as, and if their qualifications and activity justify 
such advancement. 

I want you to know that we, the Officers of the Society, are ap- 
preciative of the excellent support which we have received from the 
membership. I want the sustaining members to know that their 
support is sincerely appreciated and valued. 

Respectfully submitted, 
LOREN L. RYDER, President 



Historical Sketch of 
Television's Progress 

BY L. R. LANKES 

EASTMAN KODAK COMPANY, ROCHESTER 4, NEW YORK 



Summary This is a brief review of published material and, in its original 
form, was an introductory part of a symposium on the various aspects of 
television which will affect the photographic industry. It is not an attempt 
to answer directly the question, "Who invented television?" for, as Waldemar 
Kaempffert, Science Editor of the New York Times, has already pointed 
out, Professor William F. Ogburn in his "Social Change" has listed 148 
major discoveries and inventions which were made simultaneously and 
independently by at least two workers in the particular field concerned in 
each case; and if the list were to include developments of secondary im- 
portance, it would undoubtedly have grown into a volume at least as large 
as an unabridged dictionary. Rather, then, it should be construed as an 
attempt to convey a general understanding of the subject by considering how 
it was pieced together. 



OF ALL THE PURSUITS to which one can turn his attention, perhaps 
none has aroused a higher degree of curiosity, enthusiasm, and 
hope than the development of television. It has been said that tele- 
vision holds the promise of being the medium that can bring the 
peoples of far places emotionally face to face with one another's man- 
ners, customs, and problems, and thereby make them understand that 
they are all essentially human. It co,uld be said that the motion 
picture also holds this promise since television is essentially motion 
pictures with radio as the means of conveyance. However, there may 
be advantages in television's claim to immediacy: namely, that what 
is being viewed at the receiver is occurring now at the transmitter. 

Contrary to general opinion, the concept of television is not a twen- 
tieth-century product. Even in Biblical times abstract thinkers pre- 
dicted that it would be possible to develop the ability to see events 
occurring beyond the horizon. However, the crystallization of specific 
inventions which led to television as we know it today, began with the 
transition of the eighteenth to the nineteenth century. The first 
SEPTEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 223 



224 LANKES September 

items are Alexander Volta's electric battery, the voltaic pile; Profes- 
sor Berzelius' isolation of the element selenium; Oersted's discovery 
of the principle of electromagnetic induction ; and the efforts of Am- 
pere, Ohm, and Faraday. 

The middle of the nineteenth century might be said to have borne 
the infant, television, for in 1842 Alexander Bain, 1 an English phys- 
icist, first proposed a device to send pictures from one place to an- 
other by electric wires. Bain's plan was so correct basically that it 
embraced the fundamentals of all picture transmission, having recog-j 
nized the particular problems posed by the need for synchronization 
between transmitter and receiver. In 1847, Bakewell 2 devised a 
"copying telegraph" employing an elementary scanning device. 
Specifically, this was an instrument for transmitting writing or draw- 
ings in the form of nonconducting shellac ink on tin foil. The foil was 
then wrapped around a cylinder which rose as it rotated, thereby 
tracing out a spiral with a fixed metal needle pressing against the foil. 
At the receiver, a similar cylinder was covered with chemically treated 
paper. In 1862, Abbe Caselli 2 transmitted the first electric picture 
from Amiens to Paris. 

The latter part of the nineteenth century saw the groundwork for 
the construction of the present video industry. The light-sensitive 
properties of selenium were discovered in 1873 by a telegraph operator 
named May. 3 In a terminal station for the Atlantic cable on the 
coast of Ireland, May observed the effect of sunlight falling on selen- 
ium resistors in some of his circuits. This indicated that light values 
can be converted into equivalent electrical values. In 1875, G. R. 
Carey, in Boston, and Ayrton and Perry, in England, proposed to 
build a large mechanical eye using a plate of tiny selenium cells as the 
retina. 3 Each cell would be connected by wire to a corresponding spot 
on the receiver. Electromagnets connected to each of the small sec- 
tions of the receiver plate were to regulate the amount of light on each 
section. Many other suggestions, all very similar in principle, were 
advanced through this period. These were followed by Sir William 
Crookes' discovery of cathode rays in his famous vacuum tube. In 
1880, Leblanc 2 developed the complete principle of scanning wherein 
a picture is divided into lines and each line into tiny segments. Hertz/ 
in 1886, confirmed Maxwell's theories of electricity and discovered the 
photoelectric effect in 1887, when he noticed that a spark could be 
made to jump over a gap more readily if one of the electrodes were 
illuminated than if the event occurred in darkness. The German 



1 1)4 s TELEVISION PROGRESS 225 

Hallwachs 4 later studied the photoelectric effect systematically and 
concluded that light set free electrical particles from the electrode 
surface. Sir J. J. Thompson identified them as electrons and Einstein 
announced the theory of the photoelectric effect. The practical side 
was advanced by Elster 4 and Geitel 4 who, as early as 1890, -built 
practical photoelectric cells. Thus the method was defined by which 
a television camera would turn a picture into electricity. * 

As a noteworthy aside, Thomas Edison 5 filmed his first motion 
picture in 1889; and Marconi, 6 in 1895, sent and received his first 
wireless signals across his father's estate. 

Coincidental with these latter developments came the invention, in 
1884, by the German Nipkow 4 of the rotating scanning disk. This 
disk made use of the very significant technique, previously suggested, 
of dissecting the scene to be transmitted into points of light which 
would then be measured on a time scale in orderly fashion. Nipkow's 
work ranks high in the history of the medium because he realized so 
early a system which was not improved upon, basically, for nearly 
fifty years. 

In 1890, the Englishman Button 4 proposed a system for a television 
receiver which ranks in importance with Nipkow's system for the 
transmitter. Button's apparatus used a scanning disk and a light 
source controlled by a Kerr cell. This method of reassembling the 
image was likewise remarkable in that it was used widely in practical 
television systems for nearly forty years. 

At the turn of the century, Sir J. J. Thompson, 7 in his work to de- 
termine the charge-to-mass ratio of the electron, showed that the 
cathode ray was in reality a beam of high-speed electrons. His 
methods involved the application of both electric and magnetic de- 
flecting forces. At about the same time, Professor Braun 8 built a 
3old-cathode-ray tube. With it he could show the effect of magnetism 
3n electron beams in tracing their paths on a fluorescent screen. From 
the viewpoint of television, this was to be the means of scanning con- 
trol for Crookes' cathode rays- Amplitude control, on the other hand, 
was to come later. 

By the end of the first decade of the twentieth century, Professor 
Boris Rosing 2 had patented a television system, using a receiver re- 
sembling the modern set, based on the Braun cathode-ray tube. In 
1911, A. A. Campbell Swinton, 3 a man of great imagination and fore- 
sight, saw the possibility of television communication with variations 
Rosing's cathode-ray tubes at both transmitter and receiver. 



226 LANKES September 

Recent years have shown that Swinton actually predicted television 
apparatus as used today, having developed the theory of a cathode-ray- 
tube camera. Meanwhile, Knudson 2 had sent the first drawing by 
radio. 

Only a few of the early discoveries and inventions are directly em- 
ployed in modern television. However, the original work and inven- 
tions gave impetus to experiments in demonstrating that light could be 
converted into electrical impulses which, in turn, could be transmitted 
and later reconverted. Fortunately for television, the development of 
the radio and electrical arts coincided with the advanced phases of 
research in the fields of optics and vision. 

World War I delayed progress universally, for the next important! 
date is 1923 when Zworykin filed patent application on the first elec-j 
tronic television camera tube, the iconoscope, wherein the means fo 
scanning control, as well as for picture signal-amplitude control, were 
all self-contained on a completely electronic basis. While the idea 
had been proposed early in the art, this was the first practical mean 
of achieving it. 

At this time J. L. Baird 4 in England, and C. F. Jenkins 4 in the 
United States, working independently, produced and demonstratec 
systems of television based on mechanical scanning through the use o 
the Nipkow disk or something similar to it. The disk carried hole 
along a spiral in such a way that a scene, when viewed through a por 
tion of it, would be broken into parallel lines or arcs, thereby providing 
the means of measuring light values along the short tune-base whicl 
represented the frame interval. The pictures were mere shadow 
graphs at first, but Baird soon demonstrated television transmission o 
half-tone pictures as well as infrared television. 

This method of scanning, having serious limitations in definition, is 
not in use today, nor is the receiving system that reconstructed the 
picture by reversing the process. While the low-definition (less thai] 
60-line) images of those days may seem to have little bearing on tech 
niques which produce present-day, continuous-tone pictures in a 525 
line system, much of -the theory which makes present equipment pos 
sible was proved during this mechanical era. 

In 1927 the Bell System demonstrated the transmission of televi 
sion over substantial distances; between Washington and New York 
over wire line, and between Whippany, New Jersey; and New Yort 
over radio link. With this was published an analysis, thorough foi 
the time, of the transmission problems facing television, particularly 



1948 TELEVISION PROGRESS . 227 

the frequency bandwidth requirements which have become so char- 
acteristic of the art. 9 

The decade 1925 to 1935 produced many developments in steady 
succession. These began with the National Broadcasting Company's 
first radio network and Warner Brothers' "Vitaphone" sound-on-disk 
system synchronized with motion pictures. Concurrently, Congress 
established the Federal Radio Commission; progress continued with 
Bairds' first trans- Atlantic television picture and his first crude sys- 
tems of color and stereoscopic television; Farnsworth's system and 
Zworykin's system of all-electronic television were introduced em- 
ploying special cathode-ray receiver tubes called kinescopes; Bell 
Laboratories demonstrated television in color, delivering a picture 
of postage-stamp size; theater television was shown on screens as 
wide as 10 feet; two-way-wire television-telephone demonstrations 
were made by Bell; improved photoelectric cells and electronic tubes 
were introduced; an extensive program of field tests by the Radio 
Corporation of America was initiated starting with 240-line all-elec- 
tronic television employing radio relay, to continue right through 
the period of commercial operation ; and, finally, the 1935 announce- 
ment of the principle of frequency modulation by Edwin Armstrong. 

Through the efforts of men like Zworykin, Engstrom, and Gold- 
smith of RCA; Farnsworth; Ives and others at the American Tele- 
phone and Telegraph Company; Alexanderson of General Electric; 
Dumont; and Goldmark of the Columbia Broadcasting System, well- 
planned and well-executed programs made public participation in the 
United States possible in 1934. 

The Philips Company of Holland built the first iconoscope in 
Europe in 1935. Television transmitters appeared in places such as 
the Eiffel Tower and Stockholm. As the advance continued, A. T. 
and T. successfully demonstrated the capabilities of coaxial cables in 
I 1936. Such cables were laid from New York to Philadelphia, from 
Paris to Bordeaux, and from Berlin to Nuremberg. The first patent 
on coaxial cable was granted in England at this time and cables were 
laid from the British Broadcasting Corporation transmitter to Buck- 
ingham Palace and Victoria Station for the first direct televising of 
coronation-procession street scenes. 10 " 12 

In 1938 television signals from London, on ultra-short waves, were 
picked up on Long Island, although badly distorted. 

The point was reached wherein one saw the telecasting of plays 
from theater stages, the New York World's Fair, major-league 



228 . LANKES September 

baseball, and professional football. Meanwhile RCA introduced an 
improved television camera tube, the orthicon. It is beyond the scope 
of this paper to enumerate the many developments from that point 
to date. 

The lack of uniformity in choice of number of lines for the picture 
structure was never satisfactory to the nontechnical observer who was 
quick to compare television with motion pictures. Because of this, 
and in keeping with the steady advances, "definition" was standard- 
ized at 343 lines in 1935. Later this was raised to 441. In 1940 it was 
increased to 525 where it remains as today's standard. 

Although World War II brought an apparent period of inactivity, 
an abundance of knowledge and technical personnel grew out of 
government-sponsored radar and guided-missile programs. Acceler- 
ated research and development produced items such as the high-sensi- 
tivity image-orthicon and phosphors to withstand the bombardment 
of highly accelerated electron beams, for brighter pictures. 

The highly controversial issue of color versus black-and-white 
television brought the industry to a virtual standstill. After this was 
settled early in 1947 in favor of black-and-white, the prospective 
broadcaster, the equipment manufacturer, and the receiving-set pur- 
chaser appeared ready to invest in the fast-growing business. By 
December 31, 1947, the score totaled 12 cities with television service; 
18 stations operating and 55 licensees; 287 sponsors; 142,400 re- 
ceivers in private homes; 27,600 receivers in public places; 195,000 
total receiver production; and an estimated audience of 1,200,000 
with assurance of nationwide networks in the reasonably near future. 

BIBLIOGRAPHY 

(1) RCA Institutes, Inc., "Radio Facsimile," vol. 1, 1938. 

(2) American Television Society, Inc., "American Television Directory," 
1st Ann. Ed., 1946. 

(3) Lee de Forest, 'Television To-day and Tomorrow," Dial Press, Inc., 
New York, N. Y., 1942. 

(4) J. Porterfield and K. Reynolds, "We Present Television," W. W. Nor- 
ton and Co., New York, N. Y., 1940. 

(5) Deems Taylor, "A Pictorial History of the Movies," Simon and Schuster, 
New York, N. Y., 1943. 

(6) New York World Telegram, "Chronology of radio and television," Source: 
The National Broadcasting Company, The World Almanac 1945, p. 650. 

(7) J. J. Thompson, "Cathode rays," Phil. Mag., vol. 44, p. 293; 1897. 

(8) F. Braun, "Ueber ein Verfahren zur Demonstration und zum Studium 
des zeitlichen Verlaufs variabler Strome," Ann. Phys. und Chemie (Wied. Ann), 
New Series, vol. 60, p. 552; 1897. 



1948 TELEVISION PROGRESS 229 

(9) H. E. Ives, F. Gray, J. W. Horton, II. C. Mathes, H. M. Stoller, E. R. 
Morton, D. K. Gannett, E. I. Green, and E. L. Nelson, "Television Symposium," 
Trnnx. Amer. Inst. Elec. Eng., vol. 46, pp. 913-962; June, 1927. 

(10) British Patent No. 284,005. 

(11) K. Lake, "The coaxial cable," Telev. and Short Wave World, (known 
as Television (London), prior to 1939), vol. 10, p. 202; April, 1937. 

(12) "Special television cable," Elec. Rev. (London), vol. 120, p. 889; June 
11, 1937. 

(13) 0. E. Dunlap, "The Future of Television," Harper Brothers, New York, 
N. Y., 1942. 

(14) William C. Eddy, "Television The Eyes of Tomorrow," Prentice-Hall, 
New York, N. Y., 1945. 

(15) D. G. Fink, "Principles of Television Engineering," McGraw-Hill 
Publishing Company, New York, N. Y., 1940. 

(16) P. C. Goldmark, J. N. Dyer, E. R. Piore, and J. M. Hollywood, "Color 
television," J. Soc. Mot. Pict. Eng., vol. 38, pp. 311-353; April, 1942. 

(17) R. W. Hubbell, "4000 Years of Television," G. P. Putnam Sons, New 
York, N. Y., 1942. 

(18) M. S. Kiver, "Television Simplified," D. Van Nostrand and Company, 
NVw York, N. Y., 1946. 

(19) E. J. G. Lewis, "Television" (Dictionary), Pitman Publishing Company, 
New York, N. Y., 1936. 

(20) National Television System Committee, "Television Standards and 
Practices," McGraw-Hill Publishing Company, New York, N. Y., 1943. 

(21) Radio Corporation of America, "Collected Addresses and Papers on the 
Future of the New Art and Its Recent Technical Developments," vol. 1, 1936; 
vol. 2, 1937; vol. 3, 1946; vol. 4, 1947. 

(22) "Televiser," /. Telev., vol. 4, November-December, 1937. 



Report of SMPE 
Standards Committee 



THE BYLAWS OF OUR SOCIETY wisely provide that the chairmen of 
committees "shall not be eligible to serve in such capacity for 
more than two consecutive terms." The first of this present year con- 
stituted that limit for the writer's service as chairman of the Com- 
mittee on Standards, and so made appropriate this final reporting of 
the events of that period. At the same time it is hoped that this re- 
view, including as it does a description of the terminal status of the 
various standardization projects which were being conducted under 
the writer's general direction, may be of service to the new chairman 
and members of the Committee on Standards. Then too, the acceler- 
ating influence of the wartime period on standardization activities has 
stimulated a good deal of thinking with regard to the development of 
sound peacetime practices in this field, so that I have ventured to in- 
clude a certain amount of philosophizing in that connection. 

The prewar pace of the Committee on Standards was quite a 
leisurely one, determined in part by limited secretarial assistance from 
the Society office, but conditioned also by the general feeling that such 
a pace was altogether appropriate. In the 10-year period prior to 
Pearl Harbor, the parent Committee held an average of about three 
meetings a year. During the war the pace slackened to only one or 
two meetings a year, and it has continued at this reduced rate to the 
present time. The most important reason for this slackening of ac- 
tivity during the war was the establishment through the War Produc- 
tion Board of a number of War Committees of the American Stand- 
ards Association, which operated at an unusually high rate of speed 
and effectiveness in the development of War Standards in specific 
fields defined by joint committees of the Armed Forces. The sub- 
committees as well as the parent War Committee on Photography and 
Cinematography, Z52, were staffed in large measure with members of 
our Society, and with members of our Committee on Standards in 
particular. This war committee considered a total of 72 proposals for 
standardization, of which 61 were completely processed as War Stand- 
ards in a two-year period ending with the termination of the project 

* Presented May 17, 1948, at the SMPE Convention in Santa Monica, by F. T. 

Bowditch, retiring chairman. 

230 SEPTEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 



STANDARDS COMMITTEE 231 

in February, 1946. This high rate of activity may be compared with 
the long-time prior achievement of 44 SMPE Recommended Prac- 
tices, of which 33 had been advanced to American Standard (Z22) just 
prior to the organization of the Z52 War Committee in December, 1943. 1 
It was altogether proper that this high-priority war project should 
absorb all the standardization talent and energies of our SMPE mem- 
bership during these busy years, and it left us with a heavy portfolio 
of postwar projects for consideration as American Standards. Thus it 
was that in a meeting of ASA Sectional Committee on Motion Pic- 
tures, Z22, held in October, 1945, 22 projects were referred to the 
Committee on Standards, calling for the most part for revision of pre- 
war American Standards in view of the many changes found necessary 
in the preparation of the corresponding War Standards. This com- 
paratively large task, judged by the prewar speed rate, could not be 
handled effectively by the parent committee sitting as a whole, and so 
was assigned to six subcommittees. These subcommittees, as always, 
were appointed for the length of time necessary to complete their 
assignments, and since they are still active but now under the direction 
of a new Committee on Standards, the following detailed report seems 
in order. 

SUBCOMMITTEE ON CUTTING AND PERFORATING RAW STOCK 

A Subcommittee on Cutting and Perforating Raw Stock was es- 
tablished on November 8, 1945, under the chairmanship of Dr. E. K. 
Carver with Messrs. F. L. Brethaner, A. W. Cook, and D. R. White 
as members. This subcommittee was asked to review the following 
five American Standards from the standpoint of (a) method of presen- 
tation and (b) possible tightening of the limits for 16-mm film. 

Z22.5-1941, Cutting and Perforating Negative and Positive Raw Stock (16- 

Mm Silent) 

Z22.12-1941, Same (16-Mm Sound) 
Z22.17-1941, Same (8-Mm Film) 

Z22.34-1941, Cutting and Perforating Negative Raw Stock (35-Mm Film) 
Z22.36-1941, Cutting and Perforating Positive Raw Stock (35-Mm Film) 

Four of these projects have since been completed, and were finally 
approved by the American Standards Association on July 16, 1947. 
The remaining one, Z22.34, was given preliminary approval by the 
subcommittee but was then held open at the request of the Research 
Council of the Academy of Motion Picture Arts and Sciences, and has 
since been reassigned to the subcommittee. 



232 STANDARDS COMMITTEE September 

The Subcommittee on Cutting and Perforating Raw Stock now has 
two projects of critical importance on its agenda. One of these has to 
do with a consideration of dimensional standards for 32-mm film, 
first, with regard to the reconciliation of conflicting practices with re- 
gard to the location of the perforations, and second, with regard to the 
effects produced by inaccuracies in slitting, such that the resulting 
16-mm film is edge-guided erratically in projection. On account of the 
critical effects on sound quality so produced, this project is being 
jointly considered with the Committee on Sound. 

The other project is a more extensive review of the Z22.34-1941 
standard on cutting and perforating 35-mm negative raw stock, in 
view of the difficulties pointed out by the Research Council in securing 
accurate registration between Standard Positive and Negative film in 
the printing of color motion pictures. Because of the new fields of in- 
terest thus disclosed, Dr. Carver's subcommittee has been enlarged 
by the addition of Messrs. E. A. Bertram, A. F. Edouart, E. Fehnders, 
A. M. Gundelfinger, and W. E. Pohl. This group has been doing an 
excellent job, and I want to express my sincere appreciation to them, 
and, in particular, to Dr. Carver, who is always a tower of strength 
wherever standardization accomplishment is needed. 

SUBCOMMITTEE ON PHOTOGRAPHIC DENSITY AND SENSITOMETRY 

This subcommittee was appointed, under the chairmanship of Dr. 
D. R. White, to review the following ASA standards: 

Z22.26-1941, Sensitometry 
Z22.27-1941, Photographic Density 

Messrs. R. Kingslake, G. A. Mitchell, and M. Sweet constitute the 
other members of the subcommittee. The Density project has been 
successfully processed, and was approved September 26,. 1947, by the 
American Standards Association. The Sensitometry project ran into 
greater difficulties, but Dr. White is presently optimistic with respect 
to an early agreement. In view of this one remaining project, this 
group is now titled the Subcommittee on Sensitometry. 

SUBCOMMITTEE ON FILM SPLICES 

This committee, under the chairmanship of Mr. W. H. Offenhauser, 
Jr., was asked to revise the following ASA standards: 

Z22.24-1941, Film Splices Negative and Positive (16-Mm Silent) 
Z22.25-1941, Film Splices Negative and Positive (16-Mm Sound) 



19 IS STANDARDS COMMITTEE 233 

Messrs. E. A. Bertram, M. R. Boyer, T. R. Craig, A. W. Cook, C. 
E. Ives, L. E. Jones, M. W. Palmer, Lloyd Thompson, M. G. Towns- 
ley, and E. H. Unkles are the members of this subcommittee. A good 
deal of preliminary work has been done, leading to the publication of a 
very complete report 2 in the Society's JOURNAL in July, 1946. Com- 
ment accumulating as the result of this publication is to form the basis 
of the subcommittee's final action. 

SUBCOMMITTEE ON 16-MM AND 8-MM PROJECTOR SPROCKETS 

Under the chairmanship of Dr. Otto Sandvik, a subcommittee con- 
sisting of Messrs. H. Barnett, J. A. Maurer, L. T. Sachtleben, and M. 
G. Townsley has been assigned the task of revising the following 
American Standards : 

. Z22.6-1941, Projector Sprocket (16-Mm Film) 
Z22. 18-1941, Eight-Tooth Projector Sprockets (8-Mm Film) 

It was agreed that the 8-mm and 16-mm fields were so different 
from the 35-mm field, covering as they do a wide range of performance 
quality in both amateur and professional equipment, that this project 
could not be handled most effectively by the existing subcommittee on 
35-mm sprockets. It was agreed that the 1941 standards specified 
dimensional values which might better be left to the originality of in- 
dividual designers, and that the new standards might therefore specify 
a design practice insuring good performance with film. With this ob- 
jective in mind, Messrs. J. S. Chandler, D. F. Lyman, and L. R. Mar- 
tin did a very fine piece of work which resulted in the preparation of a 
paper 3 published for comment in the JOURNAL. However, basic dif- 
ferences of opinion in the subcommittee have so far prevented the rec- 
ommendation of a standard, the situation being substantially iden- 
tical to that described in a report of the Committee on Standards 4 
submitted by Dr. Carver over ten years ago. It. is there stated that 
"Many members feel that the Committee should not standardize 
sprockets of any sort but that their design should be left to the pro- 
jector and camera designers to achieve the best results with standard 
film." That argument still rages, and has recently precipitated a good 
deal of basic consideration as to the proper field of industrial stand- 
ardization, a subject which this present report will discuss later on. 
In the meantime, the Subcommittee on 16-Mm and 8-Mm Sprockets 
is endeavoring to determine whether that part of the original project 
essential to the interchangeability of film can be recommended for 



234 STANDARDS COMMITTEE September 

standardization. The suggestion has also been advanced that a 
method of test for the film-handling ability of a sprocket might be 
standardized, leaving full freedom for individual design, but permit- 
ting the consumer to evaluate it on a sound basis. 

SUBCOMMITTEE ON PROJECTION REELS 

This subcommittee, under the chairmanship of Dr. D. F. Lyman 
and including Messrs. H. Barnett, L. W. Davee, John Forrest, Lee 
Jones, M. G. Townsley, and R. T. Van Niman, has been assigned the 
task of reviewing the following ASA standards. 

Z22.4-1941, Projection Reels (35-Mm Film) 
Z22.11-1941, Projection Reels (16-Mm Film) 
Z22.23-1941, Projection Reels (8-Mm Film) 

It was suggested that these standards should be rewritten in the 
style employed in the dimensional aspects of the American War Stand- 
ard Specification for 16-Mm Motion Picture Projection Reels and 
Containers, Z52.33-1945. This war standard recognized certain de- 
sirable design considerations not included in the 1941 standards, such 
as the ratio of core-to-flange diameters, the specification of a flange 
diameter great enough to hold the rated film length with safety, and 
the specification of a flange separation which will neither hold the film 
too tightly nor permit lateral wandering. Difficulty is being ex- 
perienced in reconciling these requirements with the characteristics of 
equipment presently on the market, since no manufacturer is anxious 
to vote for the obsolescence of his present goods and production equip- 
ment. ' This, then, is another instance of the basic difficulties en- 
countered in design standardization, particularly in a well-developed 
field where many individual design practices are well established. 
Perhaps here too the solution will be found in the specification of a 
test method. Certainly this is to be preferred over a design standard 
which does no more than specify the range of present trade practices. 

SUBCOMMITTEE ON 8-MM AND 16-MM CAMERA AND PROJECTOR 

APERTURES 

This subcommittee consists of Mr. J. A. Maurer, chairman, with 
Messrs. M. G. Townsley, L. T. Goldsmith, H. J. Hood, W. C. Miller, 
and L. T. Sachtleben, and has been assigned the task of reviewing the 
following ASA Standards : 



1948 STANDARDS COMMITTEE 235 

Z22.7-1941, Camera Aperture (16-Mm Silent) 
Z22. 13-1941, Camera Aperture (16-Mm Sound) 
Z22.19-1941, Camera Aperture (8-Mm Silent) 
Z22.8-1941, Projector Aperture (16-Mm Silent) 
Z22. 14-1941, Projector Aperture (16-Mm Sound) 
Z22.20-1941, Projector Aperture (8-Mm Silent) 

It was suggested that consideration should be given to war stand- 
ards procedures in this field, since these went much farther in de- 
nning good engineering practice and in explaining the reasons for 
certain dimensional choices. The subcommittee has held several 
meetings and at present is hopeful of an early successful conclusion of 
this assignment. 

In addition to the six subcommittees working on ASA assignments 
growing out of wartime standardization, the Committee on Standards 
has two other active subcommittees, and a number of projects now 
under preliminary consideration. These are as follows : 

SUBCOMMITTEE ON THE PHOTOMETRIC CALIBRATION OF CAMERA 

LENSES 

This very able subcommittee is under the chairmanship of Dr. R. 
Kingslake, with a membership consisting of Messrs. F. G. Back, E. 
Berlant, J. W. Boyle, L. E. Clark, C. R. Daily, I. G. Gardner, G. 
Laube, E. B. Levinson, J. A. Maurer, A. E. Murray, J. Thompson, 
M. G. Townsley, and G. C. Whitaker. This project was suggested by 
the need of cinematographers for a lens transmission calibration of 
some sort which could be used in combination with set-lighting infor- 
mation to determine proper film exposures. The present //number 
markings are not sufficiently indicative of the light transmission of a 
lens, particularly since the advent of lens coatings. In joint meetings 
with the Research Council, it was agreed that SMPE would study this 
problem from a calibration method and apparatus standpoint, while 
the Research Council and the American Society of Cinematographers 
would continue their already active program of practical evaluation of 
proposed calibration methods. 

Dr. Kingslake has aggressively prosecuted this work to the point 
where a proposed calibration method and system of lens markings has 
been agreed to by the Eastern members of his committee, and these 
are now under review by the West Coast studio group. An early 
agreement is hoped for, which will constitute a very real technical 
service to the motion picture industry. 



236 STANDARDS COMMITTEE September 

SUBCOMMITTEE ON 35-MM PROJECTION SPROCKET DESIGN 

This subcommittee has Dr. E. K. Carver as chairman, with a mem- 
bership consisting of Messrs. H. Barnett, M. H. Bennett, M. R. Boyer, 
L. W. Davee, J. L. Forrest, C. F. Horstman, L. B. Isaac, and H. 
Rubin. They have completed a very creditable job 5 with respect to 
the standardization of a larger sprocket diameter (0.943-inch instead 
of 0.935-inch) which results in greatly reduced film wear, an item of 
substantial economic benefit to the trade. American Standard Z22.35- 
1947, was finally approved on July 16, 1947, incorporating this find- 
ing. At the same time, the ASA-Z22 Committee has recognized that 
other aspects of this standard are also in need of revision, so the sub- 
committee is being retained to extend its study of this sprocket. 

At the first of the year, therefore, the Committee on Standards had 
eight actively functioning subcommittees working on projects of in- 
terest to the industry. The following additional projects were in the 
status indicated : 

PROPOSED STANDARD FOR 35-MM FLUTTER TEST FILMS 

After their publication for comment, 6 these two proposals were re- 
cently presented to the Committee on Standards by the Committee 
on Sound, through the chairman, Dr. F. G. Frayne. Following their 
consideration (in December, 1947) in a meeting of the Committee on 
Standards, these proposals were returned to the Committee on Sound 
with suggestions for minor changes. A formal ballot on the recom- 
mendation of these proposals for final standardization is anticipated 
soon. 

16-MM AND 35-MM DAYLIGHT LOADING SPOOLS 

It has been suggested that the field of "16-Mm and 35-Mm Day- 
light Loading Spools" is in need of standardization. The Engineering 
Vice-President, Mr. J. A. Maurer, has agreed that this is a proper sub- 
ject for study, and has undertaken to secure the co-operation of a firm 
to carry the chairmanship burden of a subcommittee on this project. 

35-MM FILM CANS 

Present 35-mm film cans are of varying diameter and embossing, so 
that they do not stack conveniently nor otherwise handle to advantage 
in processing laboratories. The need for standardization is indicated 
and the Staff Engineer is conducting a preliminary survey to define 
the task better before assigning it. 



1<)4S STANDARDS COMMITTEE 237 

. 
FILM-CUING MARKS 

Film-printing laboratories, particularly 16-mm, have indicated the 
need for a uniform system of film-cuing marks, and it has been sug- 
gest ed that a representative group be organized to collect and analyze 
suggestions from the various laboratories. This project was pending 
in this form at the end of the year, and possibly should be assigned to 
the Laboratory Practices Committee. 

16-MM PRINT LENGTHS AND REEL SIZES 

The Division of Motion Pictures and Sound Recordings of the 
Nat ional Archives has suggested a need for the standardization of a 
limited number of print lengths and reel sizes to facilitate storage. 
This project is presently under review by the Staff Engineer. 

35-MM SOUND-TRACK DIMENSIONS 

A request has been received for the consideration of the five dif- 
ferent types of sound tracks from the standpoint of possible standard- 
ization. This has been referred by Mr. Maurer to the Committee on 
Sound for first consideration. 

FILM PRESERVATION 

A proposal has been made that a standard procedure for the pres- 
ervation of film for historical purposes should be worked out. An 
early proposal from the Motion Picture Project of the Library of 
Congress is anticipated, and this will be studied by the Engineering 
Committee on the Preservation of Film for recommendation to the 
'Committee on Standards. 

GLOSSARY OF MOTION PICTURE TERMS 

In 1943, Dr. John Andreas of the Technicolor Motion Picture Cor- 
poration, submitted to the Engineering Vice-President a very exten- 
sive Glossary of Motion Picture Terms. A number of copies was 
prepared, and these were circulated to members of the Committee on 
Standards for consideration as standards. This informal procedure 
gave rise to a great many comments as 'to the detail of the wordings, 
and in the submission of new terms for consideration at a rate faster 
than we were able to secure agreement on the definitions for the old 
ones. After trying several procedures, each dependent upon the dona- 
tion of a great deal of individual and member-company effort, largely 



238 STANDARDS COMMITTEE September 

* 

of an uninspiring routine nature, it was recognized that the project 
could only be advanced at a satisfactory rate with the aid of consider- 
able organizational supervision by the Society office. The project 
was thus transferred to the Engineering Secretary in 1946, and re- 
moved from the agenda of the Committee on Standards at that time. 
Since then, it has been decided that the estimated cost in time and 
money required to complete the Glossary is greater than can reason- 
ably be assumed at this time in view of other commitments. This proj- 
ect is thus altogether inactive at present. It is mentioned here so that 
the following suggestion may be presented for general consideration. 
Assuming that some sort of standard format could be agreed upon, 
the Glossary project could be established on a permanent basis 
through the formation of a Glossary Subcommittee in each Engineer- 
ing Committee of the Society. These might be correlated through a 
subcommittee of the Committee on Standards, the membership of 
which would consist of the chairmen of the other subcommittees. 
Since a Glossary is not a fixed thing, but changes from year to year as 
new arts and new usages develop, Glossary subcommittees would al- 
ways be in existence, although the personnel would be subject to 
change with each new term of the appointing officer. 

CONCLUSION 

This leads naturally into the concluding section of this report, 
which has to do with suggestions for a more effective Standards Com- 
mittee procedure, based upon both the achievements and the disap- 
pointments of the past. These comments have been arranged numer- 
ically, in an order determined by the development of the ideas pre- 
sented for consideration. 

1. The membership of the retiring Committee on Standards was 
chosen in an effort to secure a wide representation of technical ability 
in all fields of engineering interest so that competent subcommittees 
could be formed within the Committee membership. This led to the 
formation of a large, unwieldy parent committee, consisting for the 
most part of key members of the other Engineering Committees. Sub- 
committees of the Committee on Standards were thus barely dis- 
tinguishable from the associated Engineering Committees, so that it 
came to be realized that a needless duplication of organizations was 
occurring. 

As a matter of principle, therefore, it was agreed that it is in general 
unwise to form a subcommittee of the Committee on Standards in a 



1948 STANDARDS COMMITTEE 239 

field served by another Engineering Committee. If the Committee on 
Standards agrees that a technical study is needed in a particular case, 
the project should be assigned to the appropriate Engineering Com- 
mittee, unless there is some good reason to believe that its completion 
will be unduly delayed in this way. Since all major fields of interest 
are served by Engineering Committees composed of the top experts in 
their respective fields, the existence of an active group of such com- 
mittees would require the formation of very few subcommittees of the 
Committee on Standards. 

2. The Committee on Standards should therefore be chosen pri- 
marily as a policy-making group, to determine the type of study which 
each proposal for standardization is to receive. This will require the 
careful preparation of a preliminary analysis of each project, setting 
forth the nature of the present art, and discussing frankly the eco- 
nomic factors which may determine conflicting viewpoints. For in- 
stance, in a great many cases, present practices cannot all be con- 
ducted within a single standard, so that compliance is certain to cause 
hardship to whoever is outside any final agreement, while a perform- 
ance standard is naturally opposed by those who wish to operate in a 
highly competitive amateur market rather than in the higher quality 
professional field. In full recognition of such factors, it should then be 
the primary duty of the Committee on Standards to decide either (a) 
that the advantage to the industry is sufficient to require the prepara- 
tion of a standard, (b) that a further study is desirable in order to 
define the advantages of the proposal and the area of disagreement 
better, or (c) that the proposal is not a proper one for present considera- 
tion. As a matter of general policy, it is suggested that matters hav- 
ing to do strictly with interchangeability, nomenclature, and methods 
of test properly belong in the first category. On the other hand, a 
performance specification should be approached with considerably 
greater caution. 

3. The task itself should then be assigned to a presently function- 
ing Engineering Committee, if one exists in the field of interest. Only 
where this is not the case should a special subcommittee of the Com- 
mittee on Standards be established. As has already been indicated, 
this is because the personnel best suited to the task likely are already 
members of the appropriate Engineering Committee, and needless 
confusion exists if these persons are asked to serve in two capacities. 
At the same time, it is fruitless to attempt to interest the diverse rep- 
resentation required of the entire Committee on Standards in the 



240 STANDARDS COMMITTEE September 

details of a proposition confined to a single technical field, nor can a 
sound conclusion be reached in such a way. 

4. The task group thus established should be charged in accord- 
ance with the policy decision reached by the Committee on Standards. 
If the determination of a standards recommendation is decided upon, 
then the task group should be given the authority necessary to resolve 
controversial discussions. A two-thirds vote rather than a substan- 
tial unanimity might be established as the determining factor in such 
a case. If only a study is to be made the primary duty of the task 
group should be the preparation of a detailed report, completely de- 
fining all controversial aspects, with a majority recommendation with 
respect to further action. If, in the course of this study, substantial 
unanimity is reached with respect to a definite standards proposal, 
this can then be considered by the Committee on Standards. If no 
such proposal is made, then the Committee on Standards should de- 
cide whether (a) the new facts justify a policy decision that a standard 
should be established, or (b) that the task group report be given suit- 
able publicity as defining the present state of the art for the guidance 
of the industry. 

5. The Committee on Standards should seldom if ever attempt to 
review the details of a task-group recommendation ; only the broader 
implications as to the benefit of such a standard to the industry as a 
whole should receive consideration. Nothing is so discouraging to a 
capable task group as to have its hard-won compromises discarded, 
and its recommendation rejected because the same old arguments 
flare up in the parent committee. The chairman should be in a sound 
position to refuse to reopen these arguments through assurance that 
all viewpoints have already had their day in court in the task group. 
This, of course, requires the formation of a truly representative task 
group, which is essential to a worth-while result in any case. 

6. Finally, if such an ideal routine should become operative, 
the Committee on Standards would be in the very desirable position 
of devoting most of its energies to the development of a sound philoso- 
phy in the field of standardization. Viewpoints such as many of us 
have recently been expressing in correspondence would be exchanged 
around a conference table, and a basic policy developed which could 
be specially adapted to each proposal for standardization. Such an 
opportunity should result in the development of a sound attitude 
which would gain for the Society the respect and compliance of the 
industry in so far as standardization authority is concerned. 



1948 STANDARDS COMMITTEE 241 

It is realized that the foregoing is not all new, nor is it all my own. 
It merely represents present ideas of a good program for the future, 
based, as has been said, both upon the achievements and the disap- 
pointments of the past. As ex-chairman of the Committee on Stand- 
ards, my complete lack of authority in this field is fully recognized; 
and I hope that these suggestions will be considered simply for what- 
ever good may be derived from them in setting up a more definite and 
aggressive program for the future, in keeping with the splendid 
growth, not only in the size, but also in the technical responsibilities 
of our Society. 

REFERENCES 

(1) "Recommended Practices of the Society of Motion Picture Engineers," 
/. Soc. Mot. Pict. Eng., vol. 38, pp. 403-456; May, 1942. 

(2) "Report of the Subcommittee on 16-Mm Film Splices," /. Soc. Mot. Pict. 
Eng., vol. 47, pp. 1-11; July, 1946. 

(3) "Proposals for 16-Mm and 8-Mm Sprocket Standards," J. S. Chandler, 

D. F. Lyman, and L. R. Martin, /. Soc. Mot. Pict. Eng., vol. 48, pp. 483-520; 
June, 1947. 

(4) "Report of the Standards Committee," /. Soc. Mot. Pict. Eng., vol. 28, 
pp. 21-23; January, 1937. 

(5) Report of the Subcommittee on Projector Sprocket Design," J. Soc. Mot. 
Pict. Eng., vol. 45, pp. 73-75; August, 1945. 

(6) "Proposed Standard Specifications for Flutter or Wow as Related to 
Sound Records," /. Soc. Mot. Pict. Eng., vol. 49, pp. 147-162; August, 1947. 

Standards Committee 1947 

F. T. BOWDITCH, Chairman 

J. M. ANDREAS IRL GOSHAW W. H. OFFENHAUSER, JR. 

M. F. BENNETT HERBERT GRIFFIN J. D. PHYFE 

E. A. BERTRAM A. C. HARDY W. L. PRAGER 
M. R. BOYER R. C. HOLSLAG G. F. RACKETT 

F. L. BRETHAUER J. K. HILLIARD A. C. ROBERTSON 
F. E. CARLSON D. B. JOY L. T. SACHTLEBEN 
M. K. CARVER W. F. KELLEY OTTO SANDVIK 

J. S. CHANDLER* R. KINGSLAKE C. R. SAWYER 

A. W. COOK P. J. LARSEN J. A. SCHEIK 

E. D. COOK C. L. LOOTENS R. R. SCOVILLE 

L. W. DAVEE G. T. LORANCE J. H. SPRAY 

A. A. DURYEA D. F. LYMAN MONROE SWEET 

A. F. EDOUART PIERRE MERTZ LLOYD THOMPSON 

P. C. GOLDMARK W. C. MILLER M. G. TOWNSLEY 

A. N. GOLDSMITH H. W. MOYSE D. R. WHITE 

L. T. GOLDSMITH H. E. WHITE 

* Advisory Member. 



Errors in Calibration of the / Number 



BY FRANCIS E. WASHER 



NATIONAL BUREAU OF STANDARDS, WASHINGTON, D. C. 



Summary The present system of marking the diaphragm stops in terms 
of the geometric /number is subject to serious deficiencies so far as uniform 
performance for lenses set at the same marked stop opening is concerned. 
Decisions regarding the proper exposure time to use at a selected stop open- 
ing may be in error by 10 per cent for a lens whose surfaces do not have 
antireflection coatings, and by even greater amounts for a lens whose 
surfaces do have antireflection coatings. These errors arise from differences 
in the reflection and absorption losses in the lens elements themselves, de- 
partures of the measured from the nominal focal length, and departures of 
the measured diaphragm openings from the nominal diaphragm openings. 

A method is described whereby a lens can be calibrated by a light meter 
in terms of an ideal lens so that the variation in axial illumination in the focal 
plane need not exceed 2 per cent in using different lenses set to the same 
calibrated stop opening. 



PREFACE 

IN PROBLEMS OF photography where the accuracy of lens markings 
is critical in determining the proper exposure, the various errors 
to which these markings are subject is of considerable interest. The 
present report gives the magnitude of such errors that were found to 
exist in a representative group of 20 lenses having focal lengths that 
range from 1 / 2 to 47.5 inches. In addition, the results of calibration 
of these lenses by a photometric method that permits compensation 
of light losses resulting from absorption, reflection, and scattering are 
given. Values of lens transmittance for these lenses are shown. A 
method of plotting results of nominal, true, and calibrated / numbers 
is given that permits quick evaluation of the magnitude of the over-all 
error in terms of fractions of a stop. 

I. INTRODUCTION 

With the advance of photographic technology, a need has developed 
for more precise information on the light-transmitting characteristics 
of photographic objectives. In particular, a specific need exists for a 
more accurate means of marking or calibrating the lenses which em- 
ploy a variable stop for adjusting the lens speed. The usual method, 
at present, of calibrating a lens is to inscribe a scale of /numbers on the 
242 SEPTEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 



CALIBRATION OF / NUMBER 243 

diaphragm control. These / numbers are based upon certain geo- 
metric properties of the lens, and neglecting errors of marking, pro- 
vide a satisfactory means of varying the speed of the particular lens 
by definite integral steps. Unfortunately this system of marking 
takes no cognizance of differences in light-transmitting properties that 
occur among different types of lenses and in addition those differences 
that result between lenses of the same type when the surfaces of one 
have been treated to reduce reflection losses. 

This problem has been under vigorous attack for the past ten years 
and numerous methods 1-11 have been devised for the rating of lens 
speed with respect to some standard. These methods differ in such 
matters as type of light source, comparison lens or standard aperture, 
and type of light-registering device. The theoretical aspects of the 
problem have been discussed by McRae 8 and by Gardner 1 ' 2 who pro- 
posed several possible methods for calibration of a lens. In the present 
article, one of the methods described by Gardner is verified experi- 
mentally. The experimental technique is described and the variations 
in performance for 20 lenses, having focal lengths that range from 0.5 
to 47.5 inches, are shown. Attention is given to sources of error in the 
existing marked / number. Lastly, a process is described for deter- 
mining the transmittance of a lens from data obtained in the source 
of calibration. 

II. APPARATUS AND METHOD OF MEASUREMENT 

The apparatus consists essentially of a broad uniform source of 
white light, a sensitive light-measuring device, and a holder which can 
be used interchangeably either for mounting the lens under test or one 
of a series of standard diaphragms, each of which has a centrally 
located circular opening of known diameter. The arrangements of 
these elements is the same as that suggested by Gardner. 1 - 2 The rel- 
ative lens speed is determined by a comparison of the quantity of 
light flux transmitted by a lens with that transmitted by a circular 
opening. By making an appropriate series of measurements and by 
proper interpretation of their significance, the lens can be calibrated in 
terms of an "ideal" lens having 100 per cent transmittance. 

1 . Procedure for a Lens 

A lens is mounted in the holder and its axis is aligned with the center 
of the broad uniform source and the center of the small circular open- 
ing in the baffle covering the sensitive element of the light-measuring 



244 WASHER September 

device. The front of the lens faces the light source and the distance 
separating the rear nodal point of the lens and the baffle covering the 
light-sensitive element is adjusted to equality with the equivalent 
focal length / of the lens. The opening in the baffle does not usually 
exceed 1 mm except for some lenses of very long focal length in which 
cases it is kept under 0.01 /. All parts of the equipment are shielded 
so that only light from the source that passes through the lens can 
reach the light-sensitive element. 

Readings of the light meter are taken at each of the marked stop 
openings. To minimize error arising from backlash, readings are 
taken both for the condition of the setting at the marked / number 
being made with the diaphragm ring of the lens moving in the closing 
direction and with the diaphragm ring moving in the opening direc- 
tion.* The readings from these two sets of observations are averaged 
and this value is taken as the accepted reading of the light meter at a 
given marked stop opening. 

2. Procedure for the Standard Diaphragms 

The lens is replaced by one of the series of standard diaphragms 
which have centrally located circular openings with known diameters. 
The reading of the light meter is taken and the distance D, from the 
diaphragm to the baffle covering the light-sensitive element, is 
measured. This operation is repeated for several of the standard dia- 
phragms so selected that readings of the light meter are obtained 
throughout the same range of readings that were observed for the 
various marked apertures of the lens. The brightness of the source 
and the sensitivity of the light meter are kept unchanged throughout 
both parts of the experiment. To ensure constancy of brightness of 
the source, a constant-voltage transformer is used to maintain a con- 
stant voltage for the lamps that illuminate the broad uniform source. 
To minimize error, two sets of data are taken for both the lens and the 
series of standard diaphragms so intermingled that random fluctua- 
tions in the brightness of the light source and in the sensitivity of the 
light meter can be neglected. 

Ideally the diameters of the standard diaphragm openings should be 
so chosen that the same series of / numbers are present in both phases 

* Ten lenses (Nos. 10, and 12 to 20, inclusive) were calibrated in this manner. 
The remaining ten lenses were calibrated with the diaphragm ring moving in the 
closing direction only in accordance with the recommendation contained in Report 
No. 6 of the Subcommittee on Lens Calibration of the Society of Motion Picture 
Engineers on November 6, 1947. 



1948 



CALIBRATION OF / NUMBER 



245 



of the experiment. Too, the distance D should equal the equivalent 
focal length / of the lens. In practice, however, it has proved to be 
more convenient to let D differ from/ and to place more reliance upon 
the ratio D/A, where A is the diameter of the circular opening in a 
standard diaphragm. When a wide variety of lenses is being cali- 
brated, as is the case in this experiment, it is simpler to compute the 
/ number of the standard diaphragm from the ratio D/A and to deter- 
mine the performance for the conventional series of / numbers from 
the curve of light-meter reading versus / number than to attempt to 
reproduce the conventional set of / numbers by appropriate selection 
of values of D and A . 



D/ 



Fig. 1 Calibration curve for computing /number 
of standard diaphragms when the value of D/A is 
known. 



The / number for a lens is defined by the equation 

1 



/ number 



2 sin 



(D 



where a is the angle between the axis and the extreme ray of the cir- 
cular conical bundle transmitted by the lens. In the case of the stand- 
ard diaphragm, the relation connecting the measured quantities D 

and A is 

D = 1_ 

'A 2 tan a 



(2) 



Accordingly the values of the / numbers for the standard diaphragms 
can readily be computed from the known values of D/A. A suffi- 
ciently accurate determination of the / number can be made with the 
aid of a curve such as is shown in Fig. 1. To produce this curve, the 



246 



WASHER 



September 



values of the quantity, / number, D/A, are plotted as a function of 
D/A. Hence, for a given value of D/A, the increment that must be 
added thereto to yield the /number can be read easily from the graph. 
For values of D/A greater than 15, the values of D/A and / number 
are equal for all practical purposes since their difference is less than 
0.1 per cent. 

III. RESULTS OF MEASUREMENT 

When the values of the scale deflections of the light meter are plot- 
ted against the / numbers of the standard diaphragms on logarithmic 



i 

I 

I 10 



\\ 



Fig. 2 Scale deflection on light meter versus / 
number. Curve No. 1 is for the standard diaphragms. 
Curve No. 2 is for the lens under test. 



paper, the resulting curve is a straight line with a slope nearly equal 
to 2. The fact that the slope is not exactly 2 may be attributed to a 
slight departure from linearity of the response of the light meter to 
varying amounts of light indicated on the receiver. This curve, shown 
as curve 1 in Fig. 2, shows the relation between the scale deflections of 
the light meter and the /numbers of an ideal lens. 

In a like manner, the values of the scale deflection of the light meter 
are plotted against the / numbers of the actual lens on the same curve 



1948 CALIBRATION OF / NUMBER 247 

sheet. The resulting, curve, designated curve 2 in Fig. 2, is a straight 
line parallel to curve 1 but displaced laterally therefrom. This dis- 
placement shows in a striking manner the effect of light losses in the 
actual lens. A fairly close approximation of the relative light trans- 
mission of the actual lens at a given /number can be made at once, as 
it is simply the ratio of the ordinates of curve 1 and curve 2 for the 
given /number. 

It must be mentioned that while curve 1 is always a straight line, 
this is a consequence of its accurately determined / numbers. On the 
other hand, the / numbers for curve 2 are read directly from the lens 
markings and are subject to a variety of errors that will be discussed 
later in the paper. As a result of these random and systematic errors 
the points for curve 2 sometimes do not fall as close to the straight 
line drawn as could be desired. This is especially noticeable at the 
small apertures associated with the large / numbers. However, these 
variations in no way interfere with validity of the final results but are 
in fact helpful in tracking down errors in the /numbers. 

The values of the calibrated / numbers for the actual lens may be 
obtained readily from these curves. The calibrated / number is a 
term used to designate the/ number of an ideal lens (i.e., a lens having 
100 per cent transmittance) transmitting the same amount of light 
that is transmitted by the actual lens at a given marked / number. 
The terms T-aperture ratio or T stop 3 - 6 - 7 and equivalent-aperture 
ratio 1 are other designations of this same quantity. To determine 
the calibrated / number, the value of the scale deflection for a given 
marked / number of the actual lens is noted and the value of the / 
number of the ideal lens for which the same scale deflection is ob- 
tained is read from curve 1. This has been done for twenty lenses 
covering a wide range of focal lengths and / numbers. The results are 
listed in Table I. 

The unusual values of marked / numbers which are listed in the 
first column result from assigning a calibrated / number to the maxi- 
mum stop opening for each lens. The maximum stop opening of a 
lens quite frequently does not fall in the commonly accepted series of 
marked / numbers although the remaining marked / numbers of the 
lens usually do. The calibrated / numbers, in most instances, are 
larger than the marked / numbers. This is as expected because it is 
known that some of the light incident on the front surface of a lens is 
lost as a result of reflection back in the object space or by absorption 
in the glass. The considerable differences in the calibrated / numbers 



248 



WASHER 



September 



for a given marked / number indicate appreciable differences in the 
light-transmitting qualities of the various lenses. This is illustrated 
in Fig. 3 where the calibrated / numbers are plotted on semilogarith- 
mic paper for ten lenses. The values are given for the marked / num- 
bers. 4, 8, and 16. Departures as great as 1 / 9 stop opening are indicated 
in many instances. Since the departures may be in either direction 
from the marked stop opening, it is possible to select two lenses such 
that, on using each for the same scene at the same marked stop open- 
ing, the effective difference in exposure is equal to that produced by a 
change in excess of one full-stop opening. The fact that some lenses 
have calibrated / numbers less than the marked stop opening may 
seem anomalous in that it indicates a transmittance greater than 
unity. This is, however, for the most part, an indication of errors 
in the marked stop opening and will be discussed in more detail in a 
later section. 





















' 






















1 




























" 













































































LENS NUMBER 



Fig. 3 Departure of the calibrated / number 
from the marked / number at //4, //8, and //1 6 
for 10 lenses. The line separations shown are 
equal to one stop opening. 



Lens No. 7 is of especial interest in that the indicated stop openings 
are marked in T stops, consequently the values of the calibrated / 
numbers are quite close to the marked / numbers. Lenses Nos. 2, 3, 
7, 9, 11, and 20 have coated surfaces to reduce reflection losses. The 
gain in transmittance is definitely present but is somewhat obscured 
in Table I because the marked aperture ratios frequently differ from 
the true geometric-aperture ratio. 

The fact that the calibrated / number varies so much from lens to 
lens for the same nominal / number gives support to the proposition 






MEASURED VALUE OF THE CALII 


LENGTHS THAT RANGE FROM 








1 


2 


3 






17 


18 19 


20 


Marked 






f 






Number 


0.5 


0.5 


1.0 | 




19.0 


24.0 


30.0 


47.5 






1.9 


2.40 




2.09 














2.2 




















2.3 




















2.5 




2.82 
















2.7 




















2.8 


3.25 


3.13 


2.86 














3.0 




















3.5 




















4.0 


4.42 


4.45 


3.92 














4.5 




















5.6 


5.32 


6.32 


5.52 














6.8 




















7.5 




















8.0 


7.80 


8.78 


7.50 















9.5 










3 










11.0 


11.0 


11.8 


9.94 


jl 


13.6 


14.3 






12.5 














15.6 




15.0 
















16.0 


16.0 


15.4 


17.2 


13.6 




5 


19.2 


19.8 


19.3 


17.3 


22.0 


21.3 






! 


1 


25.8 


28.2 


26.7 


23.3 


32 










3 


37.6 


40.9 


39.2 


34.7 


45 










3 


50.8 


59.9 


53.4 


48.6 


64 










3 


69.6 


86.8 


79.0 


71.1 


90 










3 


98.0 


117.0 


99.0 


97.6 


128 


















143.0 



SETTINGS OF THE STOP OPENINGS IN llO PER CENT TRANSMITTANCE FOR 







Cali- 


1 | 2 


3 16 


17 | 18 | 19 


20 


brated 




f 




number 


0.5 


0.5 


1.0 .5 


19.0 


24.0 


30.0 


47.5 




2.8 


2.33 


2.48 


2.74 












4.0 


3.58 


3.60 


4.08 












5.7 


5.92 


5.10 


5.80 












8.0 


8.10 


7.24 


8.57 












11.3 


11.3 


10.5 


12.7 


*.60 










16 


16.4 


14.9 


19.1 


5.1 


13.2 


12.4 


12.8 


14.6 


22.6 


23.2 






&.6 


19.2 


18.2 


18.8 


20.6 


32 








i.9 


27.4 


25.2 


26.2 


29.0 


45 

a A 








5.2 

R Q 


39.3 

KQ ft 


35.1 

/IT Q 


37.3 

KQ A 


41.0 

CO O 



194S CALIBRATION OF / NUMBER 249 

that all lenses should be so marked that differences in light-transmit- 
ting properties are negligible for a given / number. This can be done 
from the curves shown in Fig. 2, by reversing the procedure used in 
deriving the information reported in Table I. The deflection of the 
light meter for a given / number of the ideal lens is noted on curve 1 
and the / number of the actual lens which will yield the same deflec- 
tion is read from curve 2. This can also be done by plotting the cali- 
brated / number for a lens listed in Table I against the marked / num- 
ber on logarithmic paper. The marked / number for a given cali- 
brated / number can then be read directly from the graph. This has 
been done for the same 20 lenses and the results are listed in Table 
II. This table shows the proper settings in terms of the marked / 
number so that each of these lenses will yield uniform performance 
for each of a series of calibrated / numbers. 

IV. SOURCES OF ERROR IN THE NOMINAL / NUMBER 

In addition to the light losses in the lens arising from absorption and 
reflection, there are several sources of error that affect the reproduci- 
bility in the amount of light reaching the focal plane at a given stop 
opening. The first of these is backlash in the iris-diaphragm stop and 
results in differences in light transmission dependent upon the manner 
in which the diaphragm is set at a given stop opening. The second 
error is an actual error in the markings themselves and may arise from 
errors in aperture, errors in equivalent focal length, or errors in both 
at the same time. The backlash error varies for each lens while the 
error in / markings contributes to variations in performance when 
several different lenses are in use for the same type of work. 

6 . Error in Setting the Lens at a Given f Number 

When the diaphragm is set at a given / number, there is an appreci- 
[ able difference in the amount of light passed by the lens dependent 
upon the direction of movement of the diaphragm control. The error 
arising from this source has been investigated and the results are 
listed in Table III for several lenses. This backlash error is deter- 
mined by two methods. In the first method, the lens is mounted on a 
stand and the edges of the diaphragm are illuminated from tjie rear of 
the lens by a fixed source. Photographs of the stop opening are made 
with an auxiliary camera placed in front of the lens. Each stop open- 
ing is photographed for the condition of the setting being made with 



250 



WASHER 



September 



the diaphragm closing and with the diaphragm opening. Prints are 
made of these negatives and the area of each image is measured with 
a planimeter. Let the area of the image, taken for the condition when 
the setting is made by closing the diaphragm, be Ac; and the area of 

TABLE III 

RATIOS OF RELATIVE ILLUMINATION IN THE AXIAL REGION OF THE FOCAL PLANE 
FOR LENSES USED UNDER IDENTICAL LIGHTING CONDITIONS, SETTINGS BEING 
MADE WITH THE DIAPHRAGM CONTROL MOVING TO CLOSE AND WITH THE DIA- 
PHRAGM CONTROL MOVING TO OPEN THE LENS 



Nominal 
Focal 
Length, 
Inches 


Nominal 
/ Number 


Ratio of Light Transmissions 
Diaphragm Closing to Diaphragm 
Opening 


Planimeter, 
Ac/Ao 


Light Meter, 
Lc/Lo 


Weighted 
Average 


16.5 


9.5 


1.01 


1.04 


1.03 




11 


1.01 


1.02 


1.02 




16 


1.02 


1.04 


1.03 




22 


1.02 


1.07 


1.06 




32 


1.05 


1.11 


1.10 




45 


1.13 


1.08 


1.09 




64 


1.11 


1,08 


1.09 


19.0 


11 


1.00 


1.00 


1.00 




16 


1.06 


1.02 


1.03 




22 


1.05 


1.04 


1.04 




32 


1.07 


1.06 


1.06 




45 


1.10 


1.09 


1.10 




64 


1.24 


1.26 


1.26 


24 


11 


1.00 


1.00 


1.00 




16 


1.00 


1.03 


.1.02 




22 


1.05 


1.05 


1.05 





32 


1.02 


1.11 


1.09 




45 


1.09 


1.14 


1.13 




64 


1.06 


1.18 


1.16 


30 


12.5 


0.99 


1.01 


1.00 




16 


1.04 


1.03 


1.03 




22 


1.02 


1.02 


1.02 




32 


1.04 


1.06 


1.05 




45 


1.08 


1.02 


1.03 




64 


1.08 


1.07 


1.07 



the image for the same stop opening, taken for the condition when the 
setting is made by opening the diaphragm, be Ao. Then the ratio 
Ac/Ao is t accepted as the ratio of the relative illuminations in the 
axial region of the focal plane when the lens is used under identical 
lighting conditions for these two processes of setting the lens at a 
given / number. 



1948 



CALIBRATION OF / NUMBER 



251 



In the second method, the data taken in Section II are treated in 
such manner as to separate the light-meter readings Lc, taken for the 
condition of the setting being made with the diaphragm closing, and 
the light-meter readings for the same stop opening Lo, taken for the 
condition of the setting being made with the diaphragm opening. 
Then the rate Lc/Lo is accepted as the ratio of the amounts of light 



TABLE IV 

COMPARISON OF NOMINAL AND MEASURED VALUES OF EQUIVALENT OF FOCAL 
LENGTH AND EFFECTIVE APERTURE FOR A REPRESENTATIVE GROUP OF LENSES 







Differ- 










ence 










in 


Effective 


Differ- 




Equivalent 
Focal Length 


Equiva- 
lent 
Focal 


Aperture 


ence 
in 
Aper- 




M!eas- 


Lens 


Nominal, 


Measured, 


Length, 


Nominal, 


ured, 


ture, 


No. 


Mm 


Mm 


Per Cent 


Mm 


Mm 


Per Cent 


1 


12.5 


12.35 


-1.2 


6.58 


7.07 


+7.4 


2 


. 12.5 


12.99 . 


+3.5 


5.00 


5.07 


+ 1.4 


3 


25.4 


25.56 


+ 1.0 


13.37 


13.65 


+2.1 


4 


35.0 


37.50 


+7.1 


12.96 


14.06 


+8.5 


5 


40.0 


42.08 


+5.2 


14.81 


14.94 


+0.9 


6 


50.0 


51.39 


+2.8 


18-. 52 


19.62 


+5.9 


7 


50.8 


50.62 


-0.4 


25.40 


24.40 


-3.9 


8 


75.0 


75.31 


+0.4 


26.78 


27.36 


+2.2 


9 


75.0 


75.02 


0.0 


32.61 


32.58 


-0.1 


10 


76.2 


74.71 


-2.0 


25.40 


24.60 


-3.2 


11 


101.6 


99.42 


-2.1 


39.53 


40.64 


+2.8 


12 


177.8 


180.81 


+ 1.8 


26.15 


26.15 


0.0 


13 


190.5 


190.53 


0.0 


42.34 


40.17 


-5.1 


14 


279.4 


284.85 


+2.0 


34.92 


35.74 


+2.3 


15 


342.9 


351.60 


+2.5 


45.72 


42.21 


-7.7 


16 


419.1 


418.14 


-0.2 


44.12 


41.30 


-6.4 


17 


482.6 


481.97 


-0.1 


43.87 


43.29 


-1.3 


18 


609.6 


605.55 


-0.7 


55.42 


51.40 


-7.2 


19 


762.0 


756.54 


-0.7 


60.96 


59.14 


-3.0 


20 


1206.5 


1207.60 


+0.1 









passing through the lens for these two conditions and is comparable to 
Ac/Ao obtained by the first method. 

The values of these ratios are tabulated in Table III for a series of 
stop openings for four lenses. The differences by the two methods re- 
sult mainly from the fact that a greater number of sets of data is used 
in the determination of Lc/Lo, The third column gives the weighted 



252 



WASHER 



September 



average with a weight of 4 given to Lc/Lo and a weight of 1 given to 
Ac/Ao. It is noteworthy that this error arising from backlash varies 
from 1 to 2 per cent at the larger stop openings to as high as 10 to 26 
per cent for the smaller stop openings. It is clear that error from this 
cause can be avoided by always making the diaphragm setting in the 
same manner, and preferably in the direction of closing the diaphragm. 

TABLE V 

NOMINAL AND MEASURED VALUES OF THE / NUMBER FOR A REPRESENTATIVE 

GROUP OF LENSES 



Lens 
Number 


Nominal 
Focal 
Length, 
Mm 


/ Number 


Error in 
/ Number, 
Per Cent 


Relative 
Transmit- 
tance 


Nominal | Measured 


1 


12.5 


1.9 


1.77 


-6.8 


1.15 


2 


12.5 


2.5 


2.62 


4.8 


0.91 


3 


25.4 


1.9 


1.87 


-1.6 


1.03 


4 


35.0 


2.7 


2.67 


-1.1 


1.02 


5 


40.0 


2.7 


2.82 


4.4 


0.92 


6 


50.0 


2.7 


2'. 62 


-3.0 


1.06 


7 


50.8 


2.2 


2.07 


-5.9 


1.13 


8 


75.0 


2.8 


2.75 


-1.8 


1.04 


9 


75.0 


2.3 


2.30 


0.0 


1.00 


10 


76.2 


3.0 


3.04 


1.3 


0.97 


11 


101.6 


2.5 


2.51 


0.4 


0.99 


12 


177.8 


6.8 


6.91 


1.6 


0.97 


13 


190.5 


4.5 


4.74 


5.3 


0.90 


14 


279.4 


8.0 


7.97 


-0.4 


1.01 


15 


342.9 


7.5 


8.33 


11.1 


0.81 


16 


419.1 


9.5 


10.12 


6.5 


0.88 


17 


482.6 


11.0 


11.13 


1.2 


0.98 


18 


609.6 


11.0 


11.78 


7.1 


0.87 


19 


762.0 


12.5 


12.79 


2.3 


0.96 



There still remains the random error of making the setting, even if 
care is taken to move the control always in the same direction. This 
error is, however, small in comparison to backlash error, and it is be- 
lieved that it should be negligible for the careful worker at the larger 
stop openings and perhaps rising to approximately one fourth of the 
backlash error for the smaller stop openings. 

2. Errors in the Existing Geometrical f Number 

(a) At full aperture- The true geometrical / number is obtained 
by dividing the equivalent focal length of the lens by the diameter of 



1948 



CALIBRATION OF / NUMBER 



253 



the effective aperture. It is therefore obvious that errors in the value 
of the equivalent focal length and the effective aperture will be re- 
flected by errors in the / number. Table IV lists the nominal and 



o 





1 
LENS NOI 








/ 


x 7 






LE 


JS N0.2 
5 M2 
iTEO 








i 


/'' 




f/l 


f02J 


MM 




/ 


,/ 






f/2 

CO 


5MM 




x 


^ 












/ 


/ 


















^ 












/ 


"*/ 






























/ 


* / 
















/''' 












/ 


/* 


-060 T 


RANSMI 


TTANCE 








jf 


v> 


- 0.83 


TRANSN 


ITTANC 







/ 


' / 































2 


Z 


8 4 












2 

















l.c, 




LE 


JS N0.3 
9 (=1 1 
XTEO 










/' 


K0 AND CAL 




CO 








^ 














/ 






5 "^ 
57 

40 
28 
2.0 










/ 














/I 












/ 


T^- 


087 1 


RANSM 


TTANC 


E 






// 














/'" 



















LEf 


S NQ6 

7 f-: 








V/ 


// 




1/2 


CM 




/ 


// 












4 


^7 












4 


// 












> 


// x 












X 


X- 


078 T 


RANSM 


TTANC 


- 




/ 


// 

/ 














// 

















113 16.0 22.6 



TRUE F- NUMBER 

Fig. 4 Marked and calibrated values of / number versus true geometric/ 
number. The circles indicate the marked/ numbers and the crosses indicate 
the calibrated / numbers. The circles would fall upon the dotted diagonal 
line if marked and true / numbers were equal. The crosses would fall upon 
the dotted line if the transmittance were 100 per cent. The separation of the 
dotted and solid-line curve gives a measure of the transmittance of the lens. 
The steps in the net equal one stop opening for ready appraisal of differences 
in fractions of a stop opening. 



measured values of equivalent focal length and effective aperture. 
In those instances, where the nominal focal length was given in inches, 
conversion has -been made to millimeters. The nominal values of 
effective aperture are computed from the values of nominal focal 



254 



WASHER 



September 



length and nominal / number. Examination of this table shows that 
the measured value of the equivalent focal length is within 2 per 
cent of the nominal focal length for 15 of the 20 lenses. The average 
departure for the entire 20 lenses is 1.7 per cent. The errors in 



226 




\jo 


IS NO 8 

e f-7.: 








X 


// 






LE 


MS NOl 
5 f = 4 
TED 








/ 


/ 




1/2 


CM 




y 


^ 






CO 






/<'' 














X 


X 


















2 














/ 


// 


















fl 








F-NUMBER 
J c 






x 


^ 
















/^ 












/ 


/,* 


-073 1 


RANSM 


TTANCt 










* 


^ 


085 T 


RANSMI 


TTANCE 








| 2.8 

5 
3 20 

> 


4 


JX 










































^ 
















2.8 40 57 80 1.3 160 226 320 2D 2.8 4.0 57 80 1 


3 16.0 22.6 32 ( 


NO CALIBRATE: 
i X i 




LE 


4S NO 10 

(JIN 








^ 


/ 




4 LENS NO 13 
f/45 (=7 








/ 


/ 




f/3 


/"y" 


5 IN. 




X 


// 














/ 














^ 


/ 






113 








/ 


/ X/ 
















j 


<' X/ 












X 


X/ 
















/> 
















/ 


^ 


-069 


RANSM 


TTANCE 








y 


// 


-0727 


RANSMI 


TTANCE 








V 


S/ 














/ 


/ / 
















F 










. 








// 
















*- 8 40 5.7 8.0 11.3 160 22.6 32O 450 


_8 40 5.7 80 11.3 16.0 226 32fl 45 



TRUE F-NUMBEF 

Fig. 5 Marked and calibrated values of / number versus true geometric / 
number. The circles indicate the marked/ numbers. The circles would fall 
upon the dotted diagonal line if marked and true/ numbers were equal. The 
crosses would fall upon the dotted line if the transmittance were 100 per cent. 
The separation of the dotted and solid-line curve gives a measure of the 
transmittance of the lens. The steps in the net equal one stop opening for 
ready appraisal of differences in fractions of a stop opening. 



effective aperture are as high as 8 per cent with an average for 19; 
lenses of 4 per cent. Nine of the nineteen lenses show errors in 
effective aperture in excess of 3 per cent. It is doubtful if the errors j 
in focal length can be brought below 2 per cent during the process j 



1948 



CALIBRATION OF / NUMBER 



255 



of manufacture but it does seem that the error in aperture at the maxi- 
mum aperture could also be reduced to d=2 per cent. 

As a result of these departures of the measured values of the 
equivalent focal length and effective aperture from their nominal 






640 
450 
320 
22.6 




LEF 
f/6 


IS NO 12 
8 f7 








/ 


// 


N. 




? 


~z_ 












2 


// 












/ 


// 












/ 


77 

* 










11.3 
60 
J7 




/ 


/ 


075 TRANSMITTANCE 




./ 


//' 














fl 

















LENS NO.I5 
'f/7.5 f- 13.5 IN. 



076 TRANSMITTANCE 






6O 113 16.0 22:6 320 450 640 90.0 57 80 M3 160 226 32.0 450 64X) 900 



UJ 

? 90.0 
< 

| 6 4.0 

8 

< 450 
320 
226 

16.0 
11.3 

e.o 




LENS NO. 17 






y 


y 






LEr 


IS NO. IS 








/ 


/ 


f/ll fl9 


1 




X 


77 






f/12 


IN 




} 


X 












/ 


</ 














/ 


/ 












> 


/x^ 
















/ 


X 












^ 


// 














y 


' / 












^ 


X /o 


71 TRA 


NSMIT7 


ANCE. 











y 


,X 


67 TRA 


NSMIT1 


ANCE 






; 


y 














/ 


x x> 














2 
















/ 
















ii.3 16.0 226 320 45.0 64O 900 I2i 


).0 I 


3 16.0 22.6 32.0 45.0 64.0 900 12 



TRUE f- NUMBER 



Fig. 6. Marked and calibrated values of/ number versus true geometric/ 
number. The circles indicate the marked/ numbers and the crosses indicate 
the calibrated / numbers. The circles would fall upon the dotted diagonal 
line if marked and true / numbers were equal. The crosses would fall upon 
the dotted line if the transmittance were 100 per cent. The separation of 
the dotted and solid-line curve gives a measure of the transmittance of the 
lens. The steps in the net equal one stop opening for ready appraisal of 
differences in fractions of a stop opening. 

values, appreciable errors in the / number are produced. This is 

| shown in Table V, which lists the nominal and measured / numbers 

for the same group of lenses. The errors in the / numbers range from 

6. 8 to +11.1 per cent. The effect of these errors in terms of relative 



256 



WASHER 



September 



transmittance is shown in the last column. These values of relative 
transmittance show that, neglecting losses in the lens, the difference 
between nominal / number and true geometric / number may alone 
produce deviations of as much as 19 per cent between the expected! 
and actual values of the amount of light passed by the lens. It must 
be emphasized that these differences are present at maximum stop 



TABLE VI 

NOMINAL AND ACTUAL VALUES OF THE TRANSMITTANCE AT FULL APERTURE FOR A 
REPRESENTATIVE GROUP OF LENSES 



Lens 
Num- 
ber 


Equiva- 
lent 
Focal 
Length, 
Inches 


/ Number 


Transmittance 


Marked 


True 


Cali- 
brated 


Nominal 


Actual 


1 


0.5 


1.9 


1.77 


2.40 


0.63 


0.54 


2 


0.5 


2.5 


2.62 


2.82 


0.79 


0.86 


3 


1.0 


1.9 


1.87 


2.09 


0.83 


0.80 


4 


1.4 


2.7 


2.67 


3.14 


0.74 


0.72 


5 


1.6 


2.7 


2.82 


3.14 


0.74 


0.81 


6 


2.0 


2.7 


2.62 


3.09 


0.76 


0.72 


7 


2.0 


2.2 


2.07 


2.23 


0.97 


0.86 


8 


3.0 


2.8 


2.75 


3.20 


0.77 


0.74 


9 


3.0 


2.3 


2.30 


2.45 


0.88 


0.88 


10 


3.0 


3.0 


3.04 


3.68 


0.67 


0.68 


11 


4.0 


2.5 


2.51 


2.79 


0.80 


0.81 


12 


7.0 


6.8 


6.91 


8.00 


0.72 


0.75 


13 


7.5 


4.5 


4.74 


5.60 


0.65 


0.72 


14 


11.0 


8.0 


7.97 


10.1 


0.63 


0.62 


15 


13.5 


7.5 


8.33 


9.72 


0.59 


0.73 


16 


16.5 


9.5 


10.12 


12.30 


0.60 


0.68 


17 


19.0 


11.0 


11.13 


13.60 


0.65 


0.67 


18 


24.0 


11.0 


11.78 


14.30 


0.59 


0.68 


19 


30.0 


12.5 


12.79 


15.60 


0.64 


0.67 



opening where the effective aperture is that of a true circular opening 
and not that of a many-sided opening which is operative when the 
aperture is determined by the iris diaphragm. In 6 out of 19 cases, 
the relative transmittance deviates from unity by 10 per cent or* more, 
which may produce significant differences in exposure time in someji 
instances of use. 

(6) Errors in the marked/ numbers at reduced apertures It is clean 
that errors of the type described in the preceding section are also pres-| 
ent for all of the marked / numbers. Because the aperture formed byj 



1948 CALIBRATION OF / NUMBER 257 

the usual many-leaved iris diaphragm is a polygon, the accuracy of 
determining the diameter of the effective aperture is somewhat less 
than that for the full aperture where the limiting opening is circular. 
Where the number of leaves is greater than six, two diameters at 
right angles to one another are measured and the average is considered 
to be the diameter of a circular opening of the same area. For those 
diaphragms having four to six leaves, the area is computed from two 
or three diameters, and the diameter of the equivalent circle is used in 
computing the / number. It is believed that the / number obtained 
in this manner is correct within 2 per cent for the small / numbers 
and rising to 5 per cent on the average for / numbers greater than 22. 
The errors in the /-number markings for twelve lenses are shown 
graphically in Figs. 4, 5, and 6, where the marked / numbers are plot- 
ted as ordinates and the true (measured) / numbers are plotted as 
abscissas. The dotted line with slope of unity passing through the 
origin is the line upon which the marked / numbers would lie if there 
were no error in the markings. The points are plotted on logarithmic 
paper so that one may see at a glance what the magnitude of the 
error is in terms of fractions of a stop opening. For example, in the 
case of lens No. 3, Fig. 4, the true / number corresponding to the / 
number marked 16 is 12.9. This error of marking is clearly shown on 
the graph to exceed one-half stop. For lens No. 10, Fig. 5, at //16, 
the true / number is 18.4, or more than one-half stop in the opposite 
direction. For lens No. 12, Fig. 6, the values of marked and true / 
number are very close together throughout the range of the markings. 



V. MEASUREMENT OF TRANSMITTANCE 

1. Transmittance at Full Aperture 

It is possible on the basis of the information obtained in the course 
of this experiment to determine the light transmittance of the lens 
itself. It must be emphasized, however, that the transmittance so 
determined is the ratio of the amount of light passing through the lens 
to amount of light incident on the front surface of the lens, and does 
not differentiate between image-forming and nonimage-forming light. 
There are two ways of making this determination. The first method 
yields the nominal transmittance, and is simply the square of the 
ratio of the nominal / number and the ideal / number that gives the 
same deflection on the light meter. Values obtained by this method 



258 WASHER September 

are listed in Table VI, under the heading of nominal transmit tance. 
Since no cognizance is taken of the errors in the nominal /number, the 
nominal transmittance is affected by the error in / number as well as 
by reflection and absorption losses in the lens. 

The second method yields the actual transmittance, and is the 
square of the ratio of the measured and calibrated / numbers. Since 
this method rules out the error in / number, the actual transmittance 
is affected only by reflection and absorption losses in the lens. 

It is interesting to consider lenses Nos. 16, 17, 18, and 19. These 
are all of the same type, having 8 glass-air surfaces but ranging in 
focal length from 16.5 to 30 inches. The nominal transmittance for 
these four lenses varies from 0.59 to 0.65, while the actual transmit- 
tance is almost invariant, changing from 0.67 to 0.68. 

The effect of antireflecting coatings on the lens surfaces can be seen 
in this table. Lenses Nos. 2, 3, 7, 9, and 11 are coated and all have 
transmittances which exceed 80 per cent. Only one, No. 5, of the un- 
coated lenses has a transmittance above 80 per cent and the remaining 
13 lenses have transmittances ranging from 62 to 75 per cent with one 
lens (No. 1) falling as low as 54 per cent. The antireflecting coatings 
increase the transmittance by 25 per cent or more. Even so, con- 
sideration of the actual values of the transmittance shows that 10 per 
cent or more of the incident light is still lost by the coated lens. This 
is not surprising when it is remembered that antireflecting films 
usually yield close to 100 per cent transmittance for only one wave- 
length of light. Accordingly, when a broad region of the spectrum is 
covered, as is the case for white light, the transmittance measured is 
the average for the whole region. 

The fact that the values of transmittance obtained by this pro- 
cedure are affected in some small amount by the presence of non- 
image-forming or scattered light cannot be considered as important. 
It is improbable that markedly different values would be obtained by 
the use of collimated light incident on the front surface of the lens 
during the experiment. In any comparison between the broad source 
method of measuring transmittance or calibrating a lens and the col- 
limated light method, it is unlikely that light scattered by the lens 
will produce appreciable difference in the end result. The broad 
source fills the lens with light giving rise to a greater amount of scat- 
tered light. However, the diaphragm in the focal plane rigidly re- 
'stricts the measured scattered light to that falling within a small area. 
The collimator system, at least for the larger aperture, illuminates the 



1948 CALIBRATION OF / NUMBER 259 

inner surface of the barrel with light at small angles of incidence 
favorable for reflection. All the light that is scattered and emerges 
from the lens is evaluated by the detector. A priori it is difficult to 
say which will give the most weight to scattered light. Certainly for a 
well-constructed lens the differences in results obtained by the two 
methods will be small. For a lens purposely made to reflect the light 
from the mount, the result is open to question. However such lenses 
do not constitute a threat, because they would not make satisfactory 
photographs. The extended source does give a measure of the light 
(some of which is scattered) which will be incident on a central area 
of the film when a subject is photographed with a reasonably average 
illumination over the entire field. The collimator method gives a 
measure of the light available over a central area of the film, plus all 
scattered light, when a relatively small bright source is photographed 
on a dark ground. 



2. Average Transmittance for all Apertures 

The value of transmittance obtained in the preceding section is a re- 
liable one for full aperture, but since a lens is frequently used at a re- 
duced stop opening it is advantageous to consider a method of deter- 
mining average transmittance throughout the entire range of stops. 
This is done by plotting the calibrated / number against the true / 
numbers as has been done for 12 lenses in Figs. 4, 5, and 6. The crosses 
show the relation thus obtained. It is clear that these crosses lie 
on a straight line, shown as a solid line, parallel to the dotted diagonal 
line. If the crosses should fall on the dotted line it would indicate a 
transmittance of 100 per cent. As it is, the displacement of the solid 
line from the dotted line gives at once a measure of the average 
transmittance for all apertures. This has been computed from the 
curves and the value of the average transmittance for all apertures is 
shown for each of the 12 lenses in the proper figure. 

It is worthy of mention that this method of plotting the results of 
measurement serves the dual purpose of showing the consistency of 
the method of calibration and reliability of the measured values of 
the true / number. Errors in either operation would cause the crosses 
to fall away from the solid-line curve. The fact that these deviations 
-are small indicates that both calibrated and true / numbers have been 
quite accurately assigned. 



260 WASHER 

REFERENCES 

(1) I. C. Gardner, "Compensation of the aperture ratio markings of a photo- 
graphic lens for absorption, reflection, and vignetting losses," /. Soc. Mot. Pict. 
Eng., vol. 49, pp. 96-111; August, 1947; /. Res. Nat. Bur. Stand., vol. 38, p. 
643; June, 1947, RP 1803. 

(2) M. G. Townsley, "An instrument for photometric calibration of lens iris 
scales," /. Soc. Mot. Pict. Eng., vol. 49, pp. 111-122; August, 1947. 

(3) F. G. Back, "A simplified method for precision calibration of effective 
/ stops," J. Soc. Mot. Pict. Eng., vol. 49, pp. 122-130; August, 1947. 

(4) L. T. Sachtleben, "Method of Calibrating Lenses," United States Patent 
No. 2,419,421, issued April 22, 1947, and assigned to Radio Corporation of 
America. 

(5) A. E. Murray, "The photometric calibration of lens apertures," /. Soc. 
Mot. Pict. Eng., vol. 47, pp. 142-152; August, 1946. 

(6) C. R. Daily, "A lens calibrating system," /. Soc. Mot. Pict. Eng., vol. 
46, pp. 343-357;- May, 1946. 

(7) E. Berlant, "A system of lens stop calibration by transmission," J. Soc. 
Mot. Pict. Eng., vol. 46, pp. 17-26; January, 1946. 

(8) D. B. McRae, "Measurement of transmission and contrast in optical in- 
struments," /. Opt. Soc. Amer., vol. 33, p. 229; April, 1943. 

(9) E. W. Silvertooth, "Stop calibration of photographic objectives," /. 
Soc. Mot. Pict. Eng., vol. 39, pp. 119-123; August, 1942. 

(10) D. B. Clarke and G. Laube, "Lens calibration," /. Soc. Mot. Pict. Eng., 
vol. 36, pp. 50-65; January, 1941. 

(11) D. B. Clarke and G. Laube, "Method and Means for Rating the Light 
Speed of Lenses," United States Patent No. 2,334,906, issued November 23, 1943, 
and assigned to Twentieth Century-Fox Film Corporation. 



Projection Equipment for 
Screening Rooms* 

BY H. J. BENHAM 

BRENKERT LIGHT PROJECTION COMPANY, DETROIT, MICHIGAN 

Summary Motion picture screening rooms have many and varied uses 
such as for motion picture studios, film laboratories, recording studios, film 
exchanges, and many other applications. The material to be presented 
here, however, will be concerned with screening rooms which are used in 
motion picture studios, and those in film laboratories. In many respects, 
considerably more is required of the projection equipment used in such 
screening rooms than is required when used in other types of screening 
rooms, or in regular theaters. 

UNTIL RECENTLY, standard motion picture equipment has been 
supplied for most types of screening rooms. A study of the con- 
ditions encountered, together with the experience gleaned from the 
many installations of projection equipment made in screening rooms 
during the past few years, has taught us that some modifications of 
standard equipment are desirable in order to obtain best results. It 
is important that the projection equipment used in these types of 
screening rooms perform so as not to cause any undesirable screen 
effects, which could be mistaken for errors made by the cameraman, 
or poor work on the part of the laboratory. 

Before discussing projection equipment for screening rooms, we 
should first consider the purpose of these screening rooms so that it 
will be easier to understand the reasons for some of the requirements 
demanded of the equipment, and why it is desirable to modify slightly 
some of the components used. 

The main functions of a screening room in a motion picture studio 
or a film laboratory are to check the action, direction, artist make-up, 
sequence of scenes for editing purposes, set lighting, photography, 
sound, and the laboratory processing of the film. In order to deter- 
mine how a motion picture will appear on the screen of the average 
theater, it is important that some of the conditions in the screening 
room approach closely those which are encountered in a regular 
theater. These conditions are such things as the intensity of light on 
the screen, ratio of viewing distance to picture size, and amount of 

* Presented October 16, 1945, at the SMPE Convention in New York. 

SEPTEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 261 



262 



BENHAM 



September 



ambient light. Otherwise, a picture that looks well in the screening 
room may look bad in a theater, and the opposite also can be true. 
Consideration must be given, moreover, to the difference in the mag- 
nification of the picture to determine its quality when projected on 
very large screens such as that used at Radio City Music Hall, and 
those used at drive-in theaters. 



. 

us. 




Checking Photography 

In checking the cameraman's photography, a close examinati 

must be made of the objects in the picture for steadiness and focus. 

It is important, therefore, that 
the projection equipment be free 
from vibration, be adjusted to 
prevent any lateral or vertical film 
weave, and that the projection 
lens be held firmly in focus. 
Whenever an out-of-focus con- 
dition is noticed on the screen, 
the projectionist usually is re- 
quested to check the adjustment 
of the projection lens. In order 
to check the focus of the lens 
quickly, the adjusting knob 
should be located where it is ac- 
cessible readily from either side 
of the projector mechanism. 
(Fig. 1) 

Checking Laboratory Work 

The projector must be in correct adjustment when checking the 
work done by the laboratory, because improper adjustment of the 
film guides, gate, and intermittent movement may easily result in a 
poor picture motion on the screen, which may be taken for improper 
printer registration or motion. These adjustments are important 
because a lateral movement of two thousandths of an inch of the film 
in the film trap will result in a picture movement of approximately 
three eights of an inch on a twelve-foot screen. Unless the film gate 
and guides are known to be correctly adjusted, it will be difficult to 
determine whether poor picture motion is due to the projector or to 
laboratory work. 

The main causes for flicker inherent in the film have been explained 



Fig. 1 Brenkert BX-80 projector 
mechanism showing accessibility of 
projection-lens processing knob and 
framing knob from both sides of pro- 
jector. 



1948 SCREENING-ROOM PROJECTION EQUIPMENT 263 

by Grignon, 1 as being due to one or more of three things : the original 
photography, printing, or to background projection. To determine if 
flicker is present in the picture it is important that the flicker from the 
projection equipment be negligible. Power for the arc lamp should 
have a very low ripple content, and the intensity of light on the screen 
should be kept within the limits recommended, as flicker due to the 
projector shutters becomes more objectionable as the light intensity 
is increased. 

Checking Special Effects and Relative Density 

The intensity, and the quality of the light on the screen in the 
screening room plays an important part when checking night scenes, 
subdued lighting scenes, special effects, background photography, the 
lighting of the set where the picture was photographed, the artists' 
make-up, and when judging by visual observation the optimum rela- 
tive density of each scene on the film. To check these effects correctly, 
the lighting conditions on the screen should coincide with those on the 
screen in the average theater; the intensity of light should be kept 
within the limits 2 of 9 to 14 foot-lamberts, and it should be of daylight 
quality, such as is obtained from a high-intensity arc lamp. 

CONDITIONS ENCOUNTERED IN SCREENING ROOMS 

Green Film and Film Splices 

Much of the film projected in screening rooms at film studios and 
laboratories is "green." Oftentimes difficulty is experienced when 
this film is being projected unless several precautions are taken to 
prevent the deposit of emulsion in the film trap. When emulsion does 
collect in the film trap, it usually results in difficulty in keeping the 
picture in focus, lateral and vertical picture motion on the screen, and r 
because of the increased friction of the film in the gate, torn 
sprocket holes. In order to avoid these difficulties, projectionists 
have used many expedients such as decreasing the tension on the film 
pads in the film gate, and dropping oil on the film as it passes into the 
film trap. In some cases, the emulsion deposit has been so thick and 
caused so much trouble that it has been necessary to stop the pro- 
jector before running all of the film and clean the emulsion from the 
film trap. 

In many cases the film which is projected in these screening rooms 
consists of short sequences spliced together. No modifications need be 



264 BENHAM September 

made to a well-designed projector mechanism in order to run a film 
with a large number of patches. It is important, however, that the 
gate be adjusted properly in order to minimize the picture jump when 
a patch goes through the film trap. 

Size of Screening Rooms 

Many of the screening rooms in use are very small in size, necessitat- 
ing the use of a small screen and a short "throw." Although a def- 
inite relationship should be maintained between screen width and 
viewing distance, it has been found difficult to maintain such a re- 
lationship in many screening rooms. 

In the past, low-intensity arc lamps were used almost exclusively 
for screening-room projection. Because of the small screen used in 
most cases, sufficient light could be obtained from this type of arc- 
lamp to meet the ASA recommendation of the American Standards 
Association of 9 to 14 foot-lamberts. Today, however, a large per- 
centage of pictures made are in color and the color quality of the light 
is equal in importance to the quantity of light. As a result, most of 
the screening rooms use high-intensity arc lamps and copper-coated 
Suprex carbons which produce light that has a snow-white color 
characteristic. The current range of Suprex carbons is 40 to 50 am- 
peres for the 7-mm positive and 6-mm negative, and 60 to 70 amperes 
for the 8-mm positive and 7-mm negative. The arc lamps must be 
operated- within the above ranges in order to obtain good operating 
stability. The quantity of light, however, even when the carbons are 
operated at the low end of the range, is usually more than is required 
for the small screens used at these screening rooms. Therefore, in 
order that the intensity of the light on the screen will fall within the 
recommended limits of 9 to 14 foot-lamberts, it is sometimes necessary 
to reduce the amount of light transmitted to the screen. 

EQUIPMENT FOR SCREENING ROOMS 
Projectors 

The double-shutter type of projector has been found preferable ii 
most of these types of screening rooms. However, in some cases a 
few minor modifications are desirable. The problem of emulsion 
collecting on the film shoes has been alleviated in some cases by re- 
placing in the film trap the steel film shoes with highly polished 
chrome-plated shoes. Although the steel shoes ordinarily supplied 
are highly polished and work satisfactorily with film which has been 



1948 



SCREENING-ROOM PROJECTION EQUIPMENT 



265 



properly waxed, in some cases emulsion from "green" film adheres 
more readily to polished steel shoes than to chrome-plated shoes. 

Fig. 2 shows the location of the film shoes on the film trap used on 
the Brenkert BX-80 projector. Also shown are the adjustable Holly- 
wood film guides. Accurate adjustment of these guides allows correct 
passage of the film through the film trap with negligible lateral motion 
of the film. These guides may be easily and accurately aligned by 
means of a gauge which may be purchased from the manufacturer. 




Ftfm 



If 





Fig. 2 Film trap and gate used with Brenkert BX-80 projector. All 
three sets of film- tension pads are adjusted easily and simultaneously by one 
adjusting knob. 

It can be noted in Fig. 2 that the film gate has been designed for 
three sets of film-tension pads. An equal amount of tension is applied 
to each of the two upper sets of pads, but the tension applied to the 
lower set of pads is somewhat greater, caused by the use of a heavier 
spring on the lower set of pads. The design and construction of this 
film gate aids greatly in holding the film steady in the film trap during 
the time the picture is being projected. This is especially true when a 
patch is being fed through the trap. One adjusting screw controls the 
pressure of all pads at the correct ratio. 

It was stated earlier that the use of high-intensity lamps for some 



266 



BENHAM 



September 



of the small screening rooms results in excessive screen brightness. 
One way to reduce light on the screen, and at the same time increase 
the threshold of nicker is to use three-bladed shutters on the projector 
mechanisms. Fig. 3, which is reproduced from a paper by Engstrom, 3 
shows the relationship between screen brightness and nicker rate 
when the screen is viewed at a distance of four and one half times its 
width. It also shows that nicker decreases with an increase in the 
percentage of time the image is illuminated during one frame cycle, 
and decreases with an increase in the light impulse-frequency. Inas- 
much as a three-bladed shutter increases the light impulse-frequency 
to 72 cycles, the threshold of flicker is increased considerably and the 
amount of flicker seen on a screen with a brightness of from 9 to 14 
foot-lamberts is negligible. 



One Frame- 
V 'Cycle 360' 



(fl) Double Three-Bladsd 
Shutte 



One Frame- 
Cycle 360' 




34-5 7 /<? 
Screen I// um /nation in ft Candles 




(B)Doubfe T^o-S laded 
Shutter Sy s fern 

Fig. 3 Chart showing effect of light-impulse frequency on threshold of 
flicker. Screen viewed from a distance equal to six times screen width; vision 
concentrated at center of screen. Data taken from: Proc. I.R.E., April, 
1935 (E. W. Engstrom); Soc. Mot. Pict. Eng., October, 1942 (E. W. Kellogg). 

Arc Lamps 

Where the screens are exceptionally small, the screen brightness 
will be excessive even though three-bladed shutters are used. In such 
cases, additional steps must be taken to reduce the transmission of 
light to the screen. 

One of the best methods of obtaining an additional reduction in 
light intensity is to step down the speed of the optical system in the 
arc lamp by reducing the effective area of the reflector through the 
use of a dull-black metal shield. Fig. 4 shows such a shield installed 
on a reflector from a modern arc lamp. The size of the shield depends 
on the screen brightness required. This method of reducing the 
amount of transmitted light has the advantages of protecting the 



1948 



SCREENING-ROOM PROJECTION EQUIPMENT 



267 



mirror, reducing the radiant energy on the film aperture, and improv- 
ing the depth of focus. 

Power Source 

A motor generator is preferred as a power source because of its low- 
voltage ripple content, and because it is not critical to sudden voltage 
changes. The capacity and regulation of the generator should be such 
that no change in the light intensity will be noticed on the screen when 
the second arc lamp is struck. Full- wave three-phase rectifiers are 
satisfactory, however, when used in conjunction with a projector em- 
ploying either the two- or three-bladed shutters. Four-tube rectifiers, 
designed for. operation from . a 
three-phase power source, usually 
employ a Scott-connected trans- 
; former which actually results in 
a full-wave, two-phase rectifier. 
This type of rectifier has been 
found to give satisfactory results 
when two-bladed shutters are 
used on the projectors, but an- 
noying flicker may develop when 
used in conjunction with a pro- 
jector employing three-bladed 
shutters. The reason for this is 
that a two-phase, full-wave rec- 
tifier has a voltage-ripple fre- 




Fig. 4 The effective area of the arc- 
lamp reflector can be reduced by a 
metal shield whenever a reduction of 



I quency of 240 cycles, which is an 

iexact multiple of 48 cycles but 

,_ rt light on the screen is required. 

! not of 72 cycles. The intensity 

of the ripple voltage from a two-phase, full- wave rectifier is also 
; greater than that of the three-phase, full-wave rectifier. When using 
any kind of a rectifier it is important that the alternating voltage 
across each phase be substantially the same. 

Screen 

In all cases a seamless white screen is recommended. Such a screen 
is obtainable in the sizes most frequently used. 

Although most screens have black borders, it has been found that 
light-colored borders are much more pleasing and comfortable for the 
eyes. It has been pointed out by Luckiesh and Moss, 4 that the screen 



268 BENHAM 

border should not be extremely dark because of bad physiologica 
effects such as eye fatigue. They have proved that certain eye muscles 
suffer more fatigue under conditions of dark surroundings than when 
some general lighting is available. 

The surrounding border should not be brighter than a dark area or 
the screen. This would tend to make the observer more aware of th( 
screen border than of the screen. Various shades of gray border have 
been found to be. desirable. It has been recommended that the bordei 
should be at least one thousandth to one five hundredth as bright as 
the screen high lights. 5 The contrast of a black- velvet border agains 
the screen is estimated to be from one to ten thousandths as bright as 
the screen high lights. 6 

CONCLUSIONS 

Care should be given to the selection of projection equipment fol 
screening rooms in film studios and film laboratories. 

Because of the many tests made in these screening rooms, the equipl 
ment must be kept in good adjustment at all times. 

It may be necessary to reduce the amount of light transmitted ti 
the screen when small screens and high -intensity arc lamps are used. 

Screen brightness should be checked carefully so as to determine thl 
approximate results which may be expected in the average theater. 

The motor generator is the preferred power source for both two- and 
three-bladed shutters. However, the full-wave, three-phase rectifie 
was satisfactory when used w^ith either two- or three-bladed shut t era; 

REFERENCES 

(1) Lorin D. Grignon, "Flicker in motion pictures," J. Soc. Mot. Pict. Eng\\ 
vol. 33, pp. 235-248; September, 1939. 

(2) "Standards Committee Report," J. Soc. Mot. Pict. Eng., vol. 35, p. 523 
November, 1940. 

(3) E. W. Engstrom, "A study of television image characteristics," Part ( 
Proc. I.R.E., vol. 21, pp. 1631-1652, December, 1933; Part II, Proc. I.R.Eti 
vol. 23, pp. 295-310; April, 1935. 

(4) M. Luckiesh and F. K. Moss, "The motion picture screen as a lightml 
problem," /. Soc. Mot. Pict. Eng., vol. 26, pp. 578-592; . May, 1936. 

(5) S. K. Wolfe, "An analysis of theater and screen illumination data," Ji 
Soc. Mot. Pict. Eng., vol. 26, pp. 532-548; May, 1936. 

(6) L. A. Jones, "The interior illumination of the motion picture theater, j 
Trans., Soc. Mot. Pict. Eng., No. 10, pp. 83-97; October, 1920. 



The Gaumont-Kalee 
Model 21 Projector* 

BY L. AUDIGIER 

BRITISH ACOUSTIC FILMS, LTD., LONDON, ENGLAND 

AND 

R. ROBERTSON 

A. KERSHAW AND SONS, LTD., LEEDS, ENGLAND 

Summary The main features of the design of this 35-mm model are a 
completely enclosed projector, for silence, safety, and cleanliness. The 
mechanism operates in a totally enclosed oil bath, and the equipment has 
built-in accessories such as automatic change-over and fire-quenching 
levices. 

INTRODUCTION 

HE PURPOSE of this paper is to indicate the tendency in design of 
35-mm sound-film projectors in Europe, and so that members of 
the Society could study the projector in detail, and compare it with 
current practice in the United States, the Gaumont-Kalee Company 
of Toronto brought a model to the Convention Exhibition. 

When, nearly twenty years ago, the talking film passed from the 
experimental to the commercial stage, sound-film equipment was 
aaturally designed for use with existing picture-projection equipment. 
'Sound was only an addition to the basic thing, the picture. For a 
i.ong time after the arrival of sound films there was a clear-cut line 
dividing the sound equipment from the picture equipment. The 
complete picture and sound equipment was a mating dictated by ex- 
bediency of the products of a number of different manufacturers. 

More than one designer, in Europe and America, made a logical bid 
:o end piecemeal design by producing a combined picture and sound- 
lead, but although technically such a concept was attractive, com- 
nercially it did not secure acceptance. The user's preference was for a 
|nore flexible design that permitted the retention of existing projector 
nechanisms, or of existing soundheads. 

The design of complete equipment which is to satisfy expressed 
^references both in Europe and America must take into account 

* Presented October 22, 1947, by A. G. D. West, at the SMPE Convention in 
S'ew York. 

SEPTEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 269 



270 AUDIGIER AND ROBERTSON September 

established differences between equipments originating in the two hemi- 
spheres. Thus, in Europe, for the past fifteen years, projector mech- 
anisms in the medium- and high-price groups have had oil sumps 
and automatic-pump lubrication. On the other hand, enclosure of 
the operating side has been the exception. There has, in fact, been a 
preference for the open machine which leaves the film path exposed. 
In the event of a film fire, the burning film can more easily be re- 
moved. The addition of automatically operated fire extinguishers 
of the carbon-dioxide type, which quench a fire and simultaneously 
cut the motor and the arc lamp, has been common, and in some dis- 
tricts compulsory. 

In England particularly, owing to population density, really large 
cinema theaters and large screens are relatively more frequent than in 
most parts of the world, and as smoking is universally permitted, 
illumination requirements are high. 

In the realm of vacuum tubes, there has been a tendency for each 
European country to develop types dissimilar to those of its neighbor, 
and dissimilar to North American types. Only the octal-base type 
has secured any measure of international acceptance. 

The Gaumont-Kalee 21 equipment was designed for the world mar-| 
ket, as a complete picture and sound reproducer. Its designers set 
up the following table of requirements: 

1. Picture and sound performance to satisfy recommendations of 
internationally accepted authorities. 

2. Over-all reliability to be greatest that straightforward design 
and high-grade components could attain. 

3. Accessibility, including replacement of worn or defective me- 
chanical or electrical components, to be such that unskilled personnel 
could undertake necessary maintenance work in remote locations. 

4. Complete sound channels to be built up from a minimum num- 
ber of basic panel units, and component layout to be such as to facili- 
tate comprehension of circuit function. 

5. Mechanical assembly of stand, projector, soundhead, and arc 
lamp to be conceived as a whole, and to incorporate such ancillaries as 
carbon-dioxide fire-quenching equipment, picture change-over con-f 
trol, and arc switches and meters, but major units, projector, sound-j 
head, and arc lamp, to be capable of use with other equipment. 

6. Projection lenses, coated, to have //1. 9 aperture over complete; 
range of focal lengths up to 7 inches, and design of arc lamp and pro-j 
jector to permit full use of this aperture. 



1948 GAUMONT-KALEE PROJECTOR 271 

7. Projector mechanism to have oil-bath lubrication, high-effi- 
ciency flicker shutter, and enclosure of operating side. 

8. Projector drive from soundhead to conform with American 
practice. 

PROJECTOR STAND 

As the base upon which the mechanical assemblies are erected, the 
description of the equipment commences with the stand (Fig. 1). 




Fig. 1 Operating side of assembly, all covers closed 
for operation. 

This incorporates platforms for soundhead and arc lamp, and the 
bottom spool box is an integral part. Switches for motor, exciter 
lamp, and picture change-over are grouped on a panel. A second 
panel carries arc-control switches and meters, but these may be 
omitted if not required. A door at the rear (Fig. 2) corresponding to 
the spool box door in front, gives access to the chain-driven take-up, 
and to the motor and arc switches controlled by the fire-extinguisher 
equipment. Provision is made on the front end of the stand for all 
cable entries, the internal wiring being run in the factory and terminated 



272 



AUDIGIER AND ROBERTSON 



September 



at a distribution board at the cable-entry point. Wiring arrange- 
ments are, however, sufficiently flexible to suit other installation 
requirements which may arise in practice. The stand is adjustable 
for height in 3-inch steps by insertion of distance pieces, and has a tilt 
adjustment by a concealed jackscrew, accessible through the door on 
the nonoperating side. The possible tilt varies from 10 degrees up- 
wards and from 20 to 30 degrees downwards, depending upon the 




Fig. 2 Rear view of assembly of stand, pro- 
jector, soundhead, and arc lamp. 

height of the stand. The fixed foot of the stand is a heavy iron cast- 
ing; the tilting parts, "including the spool box and doors, are all sub- 
stantial aluminum castings. 

THE SOUNDHEAD 

The soundhead bolts directly upon the horizontal upper surface of 
the stand, which also supports the driving motor, thus making a very 
rigid construction (Fig. 3). The soundhead is also arranged for the 



L948 



GAUMONT-KALEE PROJECTOR 



273 



more usual type of mounting on the back of a pedestal stand, when the 
motor is then supported by the soundhead. 

The aim motivating the soundhead design has been to secure a 
high-grade performance that will remain stable over long periods of 
time, and long life because of robust construction of all wearing rjarts. 
From the maintenance point of view the soundhead is one that can be 
kept in service for twenty years without being sent back to the fac- 
tory. Accurate jigging and dimensional uniformity of component 



; part 




Fig. 3 Rear view of assembly of stand, projector, soundhead, 
and arc lamp. Doors open and covers removed. 



s ensures that replacements will fit without requiring any tools 
other than a screwdriver and spanner. 

The soundtrack is scanned on the periphery of a rotary drum, and 
stabilization of film speed past the scanning point is maintained by a 
fluid flywheel mounted on the drum shaft (Fig. 4). The flywheel it- 
self is a light aluminum shell containing a heavy viscous fluid, a de- 
sign which eliminates the necessity for internal bearings to locate an 
inner member in respect to the outer shell. 



274 



AUDIGIER AND ROBERTSON 



September 



The optical system is of the back-scanning or visible-image type. 
Immediately in front of the exciter lamp is a large condenser which 
projects the light horizontally forward to a prism mounted partly 
within the scanning drum. The prism reverses the light path and 
directs it back through the sound track, through the objective lens, and 
on to a window carrying a mechanical slit. The window is in a hous- 1 
ing containing a prism, which directs the received light vertically 
downward on to the cathode of the phototube. As the optical mag- 
nification is six times, an enlarged image, six times that of the 




Fig. 4 Operating side of soundhead. 

actual soundtrack, is impressed on the window. With the film! 
stationary it is possible to check whether the focus is approximately j 
correct, and with the film running it is evident if either sprocket holes j 
or the edge of the picture is being projected on to the slit. The win- 
dow has fixed masks to accept the internationally accepted scanned ] 
width of soundtrack of 0.084 inch. The adjustable tracking of the| ! 
lay-on roller, centers the scanned soundtrack on the window. The| 
slit is correctly adjusted for azimuth at the factory and locked, j 1 
Various types of slits can be used with the 83 soundhead, depending j 



1948 



GAUMONT-KALEE PROJECTOR 



275 



upon the purpose for which the head is used. For re-recording, a 
very fine slit is used so that a straight-line frequency response may be 
obtained from the phototube. For all normal reproduction purposes a 
comparatively wide slit is used, because the over-all frequency-response 
curve recommended by the Academy of Motion Picture Arts and 
Sciences entails curtailment above 2000 cycles. The standard repro- 
ducing slit is 0.0108 inch wide, and taking into account the six-times 
magnification of the optical system, corresponds to a slit dimension at 
film of 0.0018 inch. This dimension results in an increased amount of 
light being passed to the phototube, with a gain in output and an in- 



._, 




Fig. 5 Rear view of soundhead; flywheel, and driving pulley removed. 

creased signal voltage on the grid of the first tube. Its effect on the 
frequency-response curve is progressively to attenuate the response 
above 2000 cycles, giving a loss of 12 decibels at 8000 cycles. 

The efficiency of the optical system is high by reason of the large 
effective aperture of all optical components. All lenses and prisms 
are hard-coated. 

All the components of the scanning system, exciter lamp, optical 
system, scanning drum, and phototube, are carried on a plate which is 
resiliency mounted within the soundhead body proper. 

There are three rotating shafts in the soundhead, the one carrying 
the fluid flywheel and scanning drum, and two which carry a film 
sprocket at one end and a gear wheel on the other (Fig. 5). These 



276 



AUDIGIER AND ROBERTSON 



Septembe 



three shafts are not carried in bearings located in the soundhead cast- 
ing, but each shaft, with its bearings, is contained in a long, flanged 
housing of circular cross section which in turn fits a machined bore in 
the soundhead casting. The flywheel shaft runs on precision ball 
bearings as it must impose a minimum load on the film. The two 
sprocket shafts run on oilite bearings as they are driven by the motor. 
When, after long service, it is necessary to renew a shaft and its bear- 
ings, the complete housing can be withdrawn by taking out three 
screws, and a new shaft and bearings, complete in a housing, replaces 
the worn components. The two assemblies of sprocket shaft, bear- 
ings, and housing are identical and interchangeable. 




Fig. 6 Soundhead dismantled. 

The whole gear train of the soundhead is carried on the two sprocket 
shafts plus one stationary layshaft. This layshaft is hardened and 
ground, and held in a machined bore in the soundhead casting. All 
the gearing is accessible when the soundhead cover is removed, and 
the complete train can be taken down in a few minutes (Fig. 6). 
Gears which rotate with their shafts are held thereto by key washers 
and end screws. 

Every component part of the soundhead, electrical, optical, and 
mechanical, down to such items as small thrust washers, carries its 
part number engraved on it. 

The complete soundhead is rustproof. The soundhead body, the 
scanning plate, and the doors are light alloy castings. The bearing 
housings, the mounts for exciter lamp, condenser and prisms, the 



1948- GAUMONT-KALEE PROJECTOR 277 

phototube housing, the slit unit plate, the brackets for lay-on and pad 
rollers, and the strippers are light alloy die castings. Small rollers 
and retaining screws are either stainless steel or chrome-plated. 

The resiliency mounted motor is carried in front of the soundhead 
with its shaft horizontal, and parallel with the sprocket shafts of the 
soundhead. The drive from motor to soundhead is by twin short can- 
vas and rubber vee belts. The motor and the belt drive are protected 
by a quickly detachable louvered cover, through which an inching 
handle projects on the operating side. Motors are available for 25-, 
30-, 40-, 50-, and 60-cycle supplies. 

For studio requirements, a three-phase synchronous or an interlock 
motor is used, and as truly synchronous speed must be maintained on 
the film sprockets, gear drive takes the place of belt drive. 

THE PROJECTOR 

The projector is not bolted directly to the top of the soundhead, but 
is mounted on a detachable base which in turn attaches to the sound- 
head; this gives flexibility to suit other soundheads and avoids the 
inconvenience which sometimes would arise, were it always necessary 
to attach the projector by bolts from beneath the soundhead into 
tapped holes in the projector base. 

American practice employs a small 17-tooth pinion which meshes 
with the projector gear train. This is an inconveniently small size, 
which, used with an oil-bath mechanism, involves an external gear 
train in order to keep the projector drive shaft at sufficient height 
above the oil level to avoid danger of oil leakage, or the employment 
of a stuffing box or equivalent expedient. -This difficulty has been 
avoided by substituting for the 17-tooth pinion one of 34 teeth, run- 
ning at the same speed and at the same relative center distance, 
thus maintaining interchangeability of soundhead drives. This 34- 
toothed pinion meshes directly with a drive gear mounted on the bot- 
tom sprocket shaft which is carried through the frame on both sides. 
This is the lowest bearing of the machine and is thus the limit to the 
amount of oil which the mechanism can contain without overflow. 

The projector body is a substantial box casting, the bottom of which 
is the oil sump. The mechanism gear train runs in an oil bath, with 
oil circulated by a gear pump and distributed after passing through a 
filter, readily detachable for cleaning. The rear cover of the machine 
has a large clear window for viewing the mechanism and the working 
of the oil distribution; a "sight" window is provided at the operating 



278 AUDIGIER AND ROBERTSON September 

side to show the correct oil level. This is marked with a series of lines 
to indicate the correct level corresponding to different angles of tilt. 
Optional positions are provided for an oil-drain plug in the front end, 
and on the nonoperating side of the mechanism, to suit different 
soundheads. The floor of the box casting is sloped internally so that 
the oil can be drained from the front, even in the case of a positive rake. 

The projector gear train comprises throughout, cast-iron pinions 
and fiber gears in pairs. All have helical teeth for quiet running and 
their ratios have been worked out to secure a "hunting-tooth" con- 
dition in each pair, conducive to quiet running. The drive to the 
shutter shaft, which is at right angles to the main train, is by 45-degree 
spiral gears. Racking or framing is effected by rotation of the inter- 
mittent unit about the sprocket axis, timing compensation being 
obtained by sliding in synchronization the spiral-driven gear on the 
shutter shaft. 

The intermittent unit has a large-size cross and cam of 2-inch 
nominal diameter. All working parts are of heat-treated-steel pre- 
cision-ground. The roller is rigidly supported on a fixed pin carried 
between cheeks on both sides. The flywheel is mounted directly 
upon the cam shaft, there being no gearing inside the unit. The 
mechanism operates inside an oil box which is constantly flooded in 
all working positions. Adequate oil-return arrangements prevent 
leakage of oil. The unit is rigidly supported in the projector in a long 
fixed quill in which it rotates for masking adjustment. The inter- 
mittent sprocket, as all the projector sprockets, is hardened and 
ground. 

The top and bottom sprocket assemblies are constructed as units 
which can be detached without dismantling. The intermittent unit 
and also the pump are similarly removable as units. .The shutter 
shaft which is supported in bearings in the frame can also be with- 
drawn without dismantling. The rest of the gear train, including the 
housing which receives the intermittent unit, is removable in the form 
of two complete subassemblies. 

Much attention has-been given to the achievement of maximum 
shutter efficiency. The light must be cut off from the screen while 
the film is moving from frame to frame, and again for an equal balanc- 
ing period in order to obtain a sufficiently high frequency of obtura- 
tion to avoid an objectionable flicker effect; hence the maximum effi- 
ciency consistent with avoidance of "travel ghost" and marked flicker 
is about 50 per cent. 



1948 GAUMONT-KALEE PROJECTOR 279 

In practice, efficiency can be increased to some extent by encroach- 
ing into the period of film movement, which also enables a correspond- 
ing reduction in the balancing cover period. This is possible by 
talking advantage of the fact that there is a small but appreciable 
period at both the beginning and end of the film movement when its 
displacement is relatively small. The amount of encroachment toler- 
able can only be determined by trial, since it is to some extent depend- 
ent upon the intensity of illumination and also upon the rate of in- 
crease in illumination which depends upon the characteristics of the 
shutter. 

Offsetting this the shutter does not cut a single ray of light, but a 
beam of sensible diameter, hence its operation cannot be instantaneous 
and the corresponding intervening twilight periods between full 
illumination and full cutoff involve some loss of potentially useful 
light, and the only effective way of increasing shutter efficiency lies in 
shortening this period. 

One method of attack, adopted in several projectors of recent design 
has been the employment of twin shutter blades rotating in opposite 
directions, thus making a scissors-type shutter which, by cutting the 
beam simultaneously from opposite sides, cuts it in one half the time 
required by the conventional single shutter. Experiments made with 
this type of shutter showed a gain in average illumination of about 15 
per cent. The current 21 projector employs a single-bladed shutter 
running at twice the normal speed. This achieves the same efficiency 
as the double shutter since it, too, cuts the light beam in one half the 
time of that taken by a normal single shutter. 

The principle has been employed in 16-mm projectors and was in 
fact used in the first Kalee projector made 37 years ago. As applied 
to the 21 projector it affords a very straightforward construction with 
avoidance of external gears and oiling points. The high shutter 
speed, 2880 revolutions per minute, demands adequate lubrication to 
ensure quiet, troublefree running. A pipe furnishes a constant 
supply of oil from the pump, and the shutter shaft has a spiral oil 
groove which pumps oil continuously through the bearing, after which 
it is again returned to the sump by a return passage, a "flinger" 
assuring that no oil escapes into the shutter casing. Since the shutter 
runs at twice normal speed it requires a single blade of approximately 
180 degrees cover instead of the usual pair of 90-degree blades. The 
blade is counterbalanced by steel plates riveted to the blade, which is 
of light-gauge aluminum. This makes a very stiff construction in 



280 



AlJDlGIER AND ROBERTSON 



September 



perfect balance. The shutter casing houses the transformer for the 
threading lamps and the magnet of the change-over unit, with asso- 
ciated wiring and fuses. 

An advantage of the open-sided mechanism is the freedom from 
restrictions imposed upon the lens holder by enclosure, which makes it 
easy to use large-diameter, big-aperture lenses. It has, however, 




Fig. 7 Operating side of projector. 



been possible to retain much of this advantage by arranging the lensj 
holder outside the enclosure (Fig. 7). The bore of the holder isjj 
standard 2.781-inch diameter and it is furnished with a removable! 
liner to take 2.062-inch diameter. The gripping length, while ade-j 
quate, is kept short and close to the film plane, and permits the use of i 
large-diameter lenses with still larger stepped-front elements. It isj 



194S GAUMONT-KALEE PROJECTOR 281 

thus possible to use //I. 9 lenses throughout the whole range of focal 
lengths up to 7 inches. 

The gate opens with a parallel action, is self-sustaining when open, 
and operated by a conveniently located handle. The front part of the 
gate assembly, which carries the spring-loaded film-guide rollers and 
pressure pads, is carried in a box-shaped casting which also receives 
the rear end of the projection lens. The gate simply hooks into a 
location in the face of this box. This construction gives utmost 
rigidity combined with accessibility as the gate assembly is instantly 
removable for cleaning. 

The gate has twin apertures; the lower one is the projection aper- 
ture, and the upper one is for verification that the film is in frame. 
When the gate is closed the stray end of a broken film cannot intrude 
into the light path. 

The whole gate assembly is detachable as a unit. A polished reflec- 
tor is provided just behind the aperture to reject the heat of overspill 
illumination and this, together with massive construction and ample 
radiating surface, assures cool operation. The mask plate is of 
hardened steel and retained in slots in the gate bracket from which it 
is quickly detachable. 

The framing aperture and the working side of the projector are 
illuminated by a pair of small low-voltage lamps. The lamps are fed 
from a transformer tapped to suit both 100/115- and 200/240-volt 
supplies. 

The safety shutter is housed in the rear of the gate unit, and is 
actuated by a centrifugal governor on the shutter shaft of the projector. 

PICTURE CHANGE-OVER 

The electrically operated picture-change-over device operates on 
the safety shutter, but in such a way that no derangement of the 
change-over system can prevent the shutter falling when the force 
exerted by the centrifugal governor fails when the machine slows down 
or stops. 

The safety shutter is raised by a floating lever acted upon inde- 
pendently by both the governor and a change-over magnet. Neither 
act ing alone can open the shutter, which can only open a.nd remain 
open so long as both exert a pull. The change-over operating mech- 
anism proper is very simple, consisting merely of a tractive magnet 
arranged to pull down an armature connected to the floating lever 
operating the shutter. Magnet core and armature are laminated and 



282 AUDIGIER AND ROBERTSON September 

fitted with slug rings, and wound for operating on alternating or 
direct current supply at mains' voltage. The magnet is in circuit 
the whole time that the picture is on the screen; change-over is 
effected by a throw-over switch which breaks the magnet circuit of 
the outgoing machine, closing the shutter, and simultaneously ener- 
gizes the magnet of the incoming machine, the shutter of which opens 
because its actuating lever is being pulled both by centrifugal and 
magnetic force. 

A two-station switch circuit is employed which allows operation 
from either machine. This can be extended for three-machine opera- 
tion. The picture change-over readily could be coupled to the sound 
change-over, but there is divergence of opinion among operators as to 
the merits of such a provision. 

FIRE CONTROL 

The Pyrene fire-extinguisher equipment comprises a sealed cylinder 
of compressed carbon-dioxide gas and a spring-loaded piercer, which 
punctures the seal and releases the gas. This piercer is held back by a 
celluloid loop. A quick-burning gun-cotton fuse instantly transmits 
a fire at any of several points along the film path to the loop which ig- 
nites and releases the piercer. Pipes conduct the gas to various 
points along the film path, effectively quenching any fire. The gas is 
also led into both top and bottom spool boxes and to pistons which 
knock off switches, cutting the power supply to both motor and lamp, 
thus shutting' down the equipment. In practice, in the event of a 
fire, not more than two frames are lost. 

THE LAMP 

The arc lamp employs a 16-inch diameter elliptical mirror with 
focuses at 6 and 36 inches. This mirror works at a larger collective 
angle than the more usual 14-inch mirror, and hence transmits more 
light. Experience has also shown that important practical advan- 
tages of its larger dimensions are that arc focus is less critical and the 
greater crater distance results in substantial freedom from pitting and 
reduced risk of mirror breakage. It has been found quite safe to 
operate this lamp at rakes of as much as 30 degrees. 

It has been possible to maintain the generally accepted optical- 
center height with this large-diameter mirror by keeping the positive- 
carbon drive to the rear of the lamphouse. This has resulted in a 
clear unobstructed floor in front of the mirror. The lamp mechanism 
is of straightforward orthodox type. The positive carbon is driven 



1948 GAUMONT-KALEE PROJECTOR 283 

directly by a variable-speed motor connected across the arc gap. 
The negative carbon is driven from the same motor through a variable- 
ratio drive comprising a cam-operated variable-stroke roller clutch. 
The complete drive unit can be withdrawn through the rear of the 
lamp. The whole of the mechanism and the mirror holder is mounted 
on a stiff cast tray which forms the base of the lamp. The lamp- 
house itself is constructed throughout of sheet steel fabricated and 
welded into a stiff one-piece shell with flush fitting doors, similarly 
fabricated. 

Knobs on the operating side of the lamp, below the door line, give 
independent manual control of positive and negative carbons. These 
have quick releases for resetting and can be clutched together by 
pressing in a push button on the rear control panel to focus the 
crater, keeping the gap constant. A periscope system contained in- 
side the lamphouse forms an image of the crater on a screen in the top 
of the lamp. A push-button strike is provided. 

A wedge-operated quick-release positive-carbon grip safeguards 
against excessive clamping force and instantly dismantles for clean- 
ing, and a tachometer shows the actual speed of the feed motor. 

SOUND AMPLIFICATION 

The complete amplifier system for a single or dual channel is built 
from basic units, all of which are mounted on cadmium-plated, rust- 
proof panels of uniform width (Fig. 8). Panels are mounted in the 
vertical plane. All components, including tubes, are on the front 
face, with terminals projecting through to the back, on which side, in 
one plane, is all the wiring (Fig. 9). Every component is rated for 
continual tropical use, and in the design, care has been taken to oper- 
ate tubes and rectifiers at less than the rating permitted by the manu- 
facturers for continuous service. Tubes used are exclusively of the 
internationally accepted and available octal-base type. 

The basic working panels comprise a three-stage preamplifier, a 
volume control, a 30-watt power amplifier, a power-supply unit, a 
meter panel, a dividing network, and exciter-lamp supply units. 
From these units a complete single-channel system can be evolved. 
A dual-channel equipment requires the addition of a switch-control 
panel, and for technical reasons, a separate unit to provide heater 
current for the tubes in the preamplifier. An optional unit, which 
can be added to either a singie-or dual-channel equipment, is a panel- 
mounted monitor and deaf-aid amplifier. 



284 



AUDIGIER AND ROBERTSON 



September 



The standard equipment is suitable for operation from 50- or 60- 
c,ycle mains of any voltage from 90 to 130 volts and from 190 to 260 
volts. Alternative power-supply and exciter-supply panels are avail- 
able which permit of direct operation from 25 cycles. These 25- 




Fig. 8 Front view of cabinet rack. 

cycle units will operate equally well from 30-, 40-, 50-, or 60-cycle sup- 
plies. Such small items as the monitor and deaf-aid panel, and the 
unit which provides heater current for the tubes in the preamplifiers, 
are made in one model only suitable for connection to mains of any 
periodicity between 25 and 60 cycles. 

A complete single-channel amplifier is housed in two main units, a 



1948 



GAUMONT-KALEE PROJECTOR 



285 



wall-mounting case for the preamplifier, and a cabinet-type rack 
for the power-amplifier power-supply unit, dividing-network, and 
exciter-supply units. Two exciter-supply units are provided so that 
any soundhead test or adjust- 
ment requiring an input to the 
exciter lamp of the idle machine 
can be made during program 
hours. 

Two small monitor speakers, 
for suspension directly over the 
two operating positions, are sup- 
plied. The level from the moni- 
tors is adjusted at the time of in- 
stallation to suit the conditions 
prevailing and the operator's 
preference, and remains there- 
after in direct relationship to 
the volume of sound emitted 
from the stage speakers. A 
monitor on-ofT switch is provided, 
and is fixed in a position adjacent 
to the telephone in the operat- 
ing enclosure. 

The equipment is completed 
by a switch-fuse distribution 
unit which is fixed to the Avail, 
alongside the main switch fuse 
terminating the alternating cur- 
rent run to the operating enclo- 
sure. This distribution unit car- 
ries a voltage-adjusting trans- 
former so that, irrespective of the 
incoming mains' voltage, the cor- 
rect voltage may be fed to the untapped primary windings of the 
various mains' transformers on the working panels. 

A dual-channel equipment duplicates both the preamplifier and the 
power amplifier. The two preamplifiers are housed in similar wall- 
mounting cases and two cabinet-type racks house the remaining 
panels. Normally each preamplifier serves one soundhead, but in 
emergency either amplifier can be switched to serve two soundheads. 




9 Cabinet rack; rear cover re- 
moved. 



286 AUDIGIER AND ROBERTSON September 

A control panel, housed in one of the racks, selects which of the two 
30- watt channels is to be used, or in a third position of the switches, 
links the two power amplifiers to give a total power output of 60 watts. 
Correct matching of the power amplifiers, both in respect of input 
impedance and output load is preserved irrespective of whether either 
channel alone or the two linked are in use. The control panel also 
carries a meter calibrated in decibels, and two gain-control switches, 
which permit the two channels to be balanced accurately for sensi- 
tivity. The meter also permits over-all frequency-response curves of 
the two channels to be measured. 

The preamplifier has three stages, resistance-capacitance-coupled 
with negative feedback over the last two stages. Adjustment of fre- 
quency response is by a unit, mounted on the amplifier panel, which 
gives independent control of bass and treble response, permitting an 
over-all curve to Academy or any other recommendation to be 
obtained. 

The main volume control is a 22-stud, click-action network with a 
stationary scale and a rotating pointer. Sound change-over is by in- 
stantaneous switch. Both volume and change-over can be remotely 
controlled from positions adjacent to the two projectors. 

The power amplifier has three stages, with negative feedback over- 
all. The power stage comprises four 6L6G tubes in parallel push-pull, 
and at the rated output of 30 watts there is less than l J /2 per cent of 
total harmonic distortion at the frequency where distortion is at a 
maximum. 

The power-supply unit is on a separate panel, both to reduce the 
weight and complexity of the power amplifier, and to permit of its 
ready interchange with the 25-cycle model. It utilizes two hard therm- 
ionic rectifiers of the 5U4G type. 

EXCITER SUPPLY 

The exciter-supply units employ selenium-type metal rectifiers, and 
the two-section, choke-input filter gives a smoothed output compar- 
able to that obtained from accumulator batteries. The direct-cur- 
rent output of each unit is controlled by the exciter-lamp switch on 
the stand carrying the projector and soundhead. The alternating- 
current input may be left connected to an unloaded unit for an in- 
definite period without harm to the rectifier or any other component. 

Throughout the design of the amplifier channel and associated 



1948 



GAUMONT-KALEE PROJECTOR 



287 



equipment, great attention has been paid to accessibility. The pre- 
amplifiers are carried on hinged frames that permit immediate access 
to the back of the panels. The cabinet-type racks have full-length 
doors in front to give access to tubes and components, and quickly 
detachable backs to give access to the wiring. Any component on any 




Fig. 10 Complete duosonic speaker assembly, small 
size. 



panel can be removed and replaced without disturbing any other 
component. All high-tension smoothing capacitors are of the steel- 
cased paper-dielectric type. 

Components which are not immediately identifiable as to type and 
value by manufacturers' markings are part numbered. All panels 
carry on their front faces a metal label giving the type number of the 
panel. 



288 



AUDIGIER AND ROBERTSON 
LOUDSPEAKERS 



September 



The loudspeaker assemblies (Fig. 10) which are of the usual two- 
way type, are supplied in four different sizes. High-frequency and 
low-frequency units have permanent magnets of Alnico 5. 

The dividing network has a crossover frequency of 500 cycles, with 

TABLE I 

PERFORMANCE OF GATJMONT-KALEE 21 PROJECTOR IN VARIOUS THEATERS IN 

GREAT BRITAIN 







O2 








3 












^ 







C3 c3 


be r "} 






0) 




3 


1 


s 


i i O> 

3 g 


2 & 


S -^ 


1 




3 "5 


Theater 


II 


1 


II 




3 a 


> 

< fe 


M ^ 


h-l CO 


11 


Astoria, 




















London, W. 


40 


62 


2400 


7,098 


2.95 


26 


3.25 


//2.2 


18 


Gaumont, 




















Princes Park, 




















Liverpool 


38 


60 


2280 


6,615 


2.90 


25 


4.25 


//1.9 


19 


Trocadero, 




















Elephant, 





















and Castle, 




















London 


40 


58 


2320 


10,887 


4.69 


25 


5.00 


//1.9 


24 


Gaumont, 




















Plymouth 


39 


59 


2301 


7,706 


3.34 


16 


4.25 


//1.9 


26 


Dominion, 




















London, W. 


40 


58 


2320 


6,425 


2.64 


18 


5.75 


//1.9 


23 


Classic, Belfast 


38 


58 


2204 


6,542 


3.42 


17 


5.00 


//1.9 


23 


Gaumont, 




















Birmingham 


38 


60 


2280 


8,658 


3.79 


16 


4.25 


//1.9 


27 


Gaumont, 




















Coventry 


41 


58 


2378 


7,581 


3.14 


16 


4.50 


//1.9 


24 


Picture House, 




















Glasgow 


42 


61 


2562 


8,114 


3.20 


20 


5.00 


jf/1.9 


23 



a 12-decibel-per-octave loss on each side of that frequency. An at- 
tenuator with five 2-decibel steps is provided to equalize the acous- 
tic output of high- and low-frequency horns. 

The high-frequency horns are of all-metal construction, with from 
eight to eighteen cells, according to the horizontal and vertical angles | 
to be covered. 

The low-frequency horn is of the direct-radiation pattern with no 



HMS GAUMONT-KALEE PROJECTOR 289 

hack emanation. In the larger sizes of horn, where the number of 
low-frequency units employed would result in a departure from opti- 
mum-load conditions, an impedance-matching transformer is used. 
The design of the low-frequency horn is such that, in addition to the 
normal back access to the low-frequency units, side access is provided 
as well. This permits the loudspeaker assembly, where backstage 
room is limited, to be positioned close against a rear wall without im- 
pairing accessibility of the units. 

THEATER PERFORMANCE 

Some measurements of light efficiency, taken at various theaters in 
London and the provinces, are shown in Table I. These indicate an 
average performance as follows: 

Arc watts 2400 

Total lumens of light output ' 8000 

Lumens per watt 3.3 

Average illumination on a 23-foot-wide screen (projector running 

with no film in the gate), foot-candles 20 

Average brightness on a 23-foot-wide screen, foot-lamberts 14 

Screen efficiency, per cent 70 

NOTE BY G. T. LORANCE 

When I was informed that the Chairman of the Board of Editors 
had suggested that "perhaps it would be interesting to publish with 
the paper a short note by Mr. Lorance discussing points wherein 
British practice differs from that in this country," I felt quite compli- 
mented and indicated my willingness to write such a note. It was not 
until I received a copy of the paper by Messrs. Audigier and Robert- 
son and began to study it that I got into trouble because it was clear 
that the authors have already well covered the points which I was 
supposed to emphasize. 

At the risk of appearing to have developed a philosophical outlook, 
let me first say that this is one of those cases, when, in comparing the 
Gaumont-Kalee machine with American machines, an introvert would 
find many, many similarities and an extrovert would find many, 
many differences. To the introvert this is still a projector, a sound- 
head, a motor, magazines, and an arc lamp mounted on a pedestal 
much as they have always been designed and mounted. To the ex- 
trovert this new assembly of equipment with the design of each piece 
correlated to the design of its associated pieces and with certain new 
details and with emphasis on them, this is a new projector and sound 



290 AUDIGIER AND ROBERTSON September 

system. Neither viewpoint, of course, is the correct one and in what 
follows I shall endeavor to find a reasonable middle ground. 

Audigier and Robertson refer to attempts to produce a combined 
sound and picture head, indicating that such a concept was technically 
attractive but commercially unacceptable and that the user preferred 
a more flexible design that allowed combinations of equipment from 
various sources and at various times. I cannot help but agree with 
the authors regarding the attractiveness, from a technical standpoint, 
of a combined design. I think they must have had it very much in 
mind because the design which they describe in this paper represents 
to me a very determined and worth-while endeavor to have your cake 
and eat it too, in that they have striven for a unified and co-ordinated 
over-all assembly of major components but have retained much of the 
familiar breakdown into major components. Incidentally, it seems 
reasonable to state at this time that, in portable and semiportable 
equipment, unified designs of a combination of projector, soundhead, 
and arc have been commercially successful for a number of years and 
that the performance of some of these unified equipments compares 
quite favorably with the performance of equipment of the regular 
type as designed for permanent installation in projection rooms. 

By and large this new Gaumont-Kalee equipment appears to follow 
pretty generally accepted American practice although it has been, of 
course, modernized in detail. A few points. are enumerated and dis- 
cussed below. An attempt has been made to restrict them to points 
of difference or to points of interest about which more knowledge 
would be of value. 

SOUNDHEAD 

Rear scanning, similar in principle to that employed in the Gau- 
mont-Kalee soundhead, has been used in American equipment. It is 
possible, of course, to do good work with either front or rear scanning 
and it is necessary to know more than is disclosed in this paper before 
we would know if this system represents an improvement over Ameri- 
can systems. 

The use of a slit image 0.0018 inch high at the film represents a de- 
parture from American practice that may be open to question. The 
desire to utilize the dropping high-frequency response of such a slit 
image as part of the desired over-all reproducing-system response char- 
acteristic is understandable. It may, however, result in other unde- 
sirable effects, such as irregular, rather than steady reproduction of 



1948 GAUMONT-KALEE PROJECTOR 291 

high frequencies. In my opinion, a slit image height of 0.0012 inch, as 
used in much American equipment, is a little larger than is desirable if 
quality of reproduction is to be stressed. 

To the best of my knowledge, commercially available American 
equipment has not used a fluid flywheel as described in this paper. 
While realizing that the fluid flywheel eliminates the necessity for in- 
ternal bearings, the quality of which is extremely critical, American 
designers apparently have not yet given favorable consideration to the 
fluid flywheel. This probably is because of a belief that to maintain 
or improve -on performance, a much larger fluid flywheel would be 
needed. Quantitative information on the performance of this 
soundhead with this size of fluid flywheel would be of interest. 

THE PROJECTOR 

The description of the use of a 34-tooth pinion for the 17-tooth 
pinion is not entirely clear to me . If, however, it provides for a higher 
oil level in the projector without decreasing the speed of the pro- 
jection drive shaft it may well represent a new and improved solution 
to this general problem. 

There is much more to shutter efficiency than the authors of this 
paper have taken time and space to present. The use of a single- 
bladed shutter, such as described, rotating at 2880 revolutions per 
minute is one method of attack which has, to the best of my knowl- 
edge, not yet appeared commercially in American machines. Fac- 
tors affecting shutter efficiency involve such things as the number of 
blades on the shutter, whether it is double or single, speed of rotation, 
diameter of the shutter, and size of the light beam where the shutter 
cuts it. Circumstances do not permit enlargement upon this thought 
in this note. 

While the lens holder is, dimensionally, in line with current Ameri- 
can practice, there are indications that American designs may adopt a 
larger lens diameter. At least one projector has been shown with 
facilities for clamping a lens having a diameter of approximately 4 
inches. 

PICTURE CHANGE-OVER 

From a technical standpoint it seems quite feasible to use the safety 
shutter as the change-over as well and such a design probably does 
simplify the complete system. 



292 AUDIGIER AND ROBERTSON September 

FIRE CONTROL 

To me, the use of built-in fire extinguisher equipment is novel in so 
far as American equipment is concerned. The subject in general is of 
such a controversial nature and exact and reproducible data are so 
difficult to obtain that I do not feel competent to comment further on 
this point. 

THE LAMP 

More information of a definite nature would be appreciated regard- 
ing the lamp. We are not informed regarding the optical speeds in- 
volved nor are we informed regarding the size of the carbons, conse- 
quently we are unable to comment accurately on the performance of 
the lamp. 

SOUND AMPLIFICATION 

While the available output power is stated, there does not appear to 
be any statement regarding the noise level. 

LOUDSPEAKERS 

An unusual point is noted in regard to loudspeakers in that the de- 
sign of the low-frequency horn is such that access to the low-fre- 
quency units is provided through the side as well as through the back 
of the horn. This is a detail which should be noted by American de- 
signers. 

THEATER PERFORMANCE 

Figures are quoted regarding the amount of light put on the screen. 
Information regarding the distribution of light on the screen would 
also have been of interest. Reference should be made to the recently 
published results of a survey by the Screen Brightness Committee,* 
which gives in considerable detail the performance of a variety of 
equipments in some eighteen American theaters. 

In conclusion, may I state the hope that the above remarks will be 
taken as being well intentioned. Messrs. Audigier and Robertson 
have developed and designed some very interesting equipment which, 
in my opinion, is well worthy of study by American engineers. 
* /. Soc. Mot. Pict. Eng., vol. 50, pp. 260-274; March, 1948. 

REPLIES BY AUTHORS TO QUERIES RAISED 

ARC LAMP 

The optical speed is //1. 9, to match the aperture of the projection 
lens. Carbon sizes used for results given in Table I were 8-mm 
positive and 7-mm negative, of "POOL" high-intensity type. (In 



1948 GAUMONT-KALEE PROJECTOR 293 

Great Britain during the war the number of types of carbons was 
greatly reduced, and the product of all manufacturers pooled.) 

INTERMITTENT SPROCKET 
The diameter is 0.945 inch. 

SOUND AMPLIFICATION 

This paper has failed to give a clear impression of the physical 
layout of the complete amplifier channel. The three-stage pre- 
amplifier is a separate unit, mounted on the wall centrally between 
the two machines, so that the circuit from the phototubes to the input 
of the preamplifier is not unduly lengthy. 

Low-capacity concentric cable is employed, and the ratio of photo- 
tube-lead capacitance to total amplifier input capacitance is such that 
a difference in length of several feet between the right-hand and left- 
hand cell lead will result in a negligible disparity in the over-all re- 
sponse curves of the two machines. The change in frequency charac- 
teristic is less than 1 decibel at 8000 cycles for a 6-foot difference in 
phototube-lead length. 

The total amplifier noise level under normal operating conditions 
is between 30 and 35 decibels below 0.006 watt. 

SCANNING SLIT 

Before adopting the wide slit, experiments were conducted with 
slit widths of from 0.0004 to 0.0018 inch (equivalent at film), and 
shaping the response curve by means of a wide slit was not found to 
impair reproduction as compared with the alternative method of 
shaping the amplifier's frequency response. 

The wide slit has been used consistently since 1939. 

FIRE CONTROL 

Accumulated practical experience of the carbon-dioxide fire con- 
trol, which has been an in-built feature of Gaumont-Kalee design 
since 1939, shows that a film fire originating anywhere in the picture 
mechanism is extinguished within less than one second of its incep- 
tion, with a loss not exceeding two frames of film, and that the action 
of the device is certain if charged and set. 



Zoomar Lens for 35-Mm Film* 

BY F. G. BACK 

RESEARCH AND DEVELOPMENT LABORATORY, 381 FOURTH AVE., 
NEW YORK 16, NEW YORK 



Summary The 35-mm Zoomar is at present mainly used for newsreel 
work where it has proved itself a valuable tool especially in the field of 
sports shots. A studio Zoomar of more rigid construction and higher opti- 
cal correction which can also be used for color work is in preparation. 

THREE ARTICLES 1 ~ 3 dealing with the basic principle of the Zoomar 
lens have already been published in this JOURNAL, so it is hardly 
necessary to go into theoretical details again. The 35-mm Zoomar has 
already established its place as a valuable tool in newsreel photog- 
raphy one year after appearance of its smaller brother, the 16-mm 
Zoomar. 

Numerous newsreel companies are using it regularly for their sport 
shots. Fast sports, especially, change their center of interest rapidly 
from one single player to a large group or even to the entire field. This 
demands the use of a Zoomar lens because the standard turret does not 
give satisfactory results. While changing lenses breaks the continuity 
and makes the picture jumpy and confusing, the Zoomar gives a con- 
tinuous transition which makes it easier to understand the game. It 
is even possible to follow the players or participants over the whole 
field and nevertheless keep them always the same size on the screen 
regardless of their position. This is of great importance in certain 
sports such as racing, football, and baseball. This striking effect 
cannot be obtained by any other means. 

The 35-mm Zoomar was primarily developed for use of newsreel 
photography with emphasis on sports, because it was almost impos- 
sible up to then to catch the high lights of a game except by accident. 

It is self-evident that the 35-mm Zoomar lens for studio work has to 
fulfill other requirements than the newsreel Zoomar. Each one will 
have to be designed differently. The lens for news photography has to 
be comparatively light in weight. It has to be capable of rapid transi- 
tion but it works only for black-and-white. The studio lens on the 
other hand may be much heavier but has to be more rigidly con- 
structed because it must be suitable for taking unconscious zooms 
* Presented October 21, 1947, at the SMPE Convention in New York. 
294 SEPTEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 



ZOOMAR LENS 



295 



which are never demanded of the newsreel Zoomar. The picture 
quality of the studio lens has to be superior to that of the newsreel 
lens, and above all the studio lens must be suitable for both black-and- 
white and color. 

Fig. 1 shows the 35-mm newsreel lens mounted on an Akeley 
camera. The coupled Zoom viewfinder is of the same basic design as 
the one in the 16-mm sport Zoomar. The cameraman is not confined 
to a fixed position to view the finder image. He sees the finder frame 
comparatively large and free from any ground-glass diffusion. 




1 



Fig. 1 



A parallax adjustment of the viewfinder was not provided, for a very 
good reason. Practical experience has shown that better results are 
obtained when the cameraman is trained to make allowances for the 
parallax instead of operating a parallax adjustment, because the tar- 
get changes its distance from the camera and therefore a parallax 
adjustment will have to be reset continuously throughout the take. 
Actually, this is never done, and therefore the framing of a viewfinder 
with parallax adjustment is not only inaccurate most of the time but 
this inaccuracy changes continuously. The Zoomar finder has a fixed 
parallax of five inches which is always maintained regardless of the 
Zoom position and of the object distance. Once the cameraman has 
learned to take these five inches into consideration he will never fail. 






296 BACK September 

The specifications for the 35-mm newsreel Zoomar are : 

Aperture range : //4.5 to //22 

Zoom range: Interchangeable wide-angle front lens, 2 to 7 inches. 

Zoom range: Interchangeable telephoto front lens, 3.5 to 13 inches. 

Field coverage: Difference in field area in any one continuous shot, 15 times. 

Object distance: From 12 feet to infinity. 

Height: 3 inches 

Length: 26 inches 

Width: 8 inches, including viewfinder 

Weight: 11 pounds, including viewfinder 

The design for the 35-mm Zoomar for studio work has not yet been 
completed. There is also a special Zoomar for animation work in prep- 
aration. 

Without doubt the 16- and 35-mm Zoomar lens have proved their 
merits and have stimulated enthusiastic cameramen to develop many 
new ideas for their uses in a variety of fields. These pioneers will 
eventually develop a new technique which will prove a valuable con- 
tribution to the art of motion picture production. 

REFERENCES 

(1) Frank G. Back, "A positive vari-focal viewfinder for motion picture 
cameras," /. Soc. Mot. Pict. Eng., vol. 45, pp. 466-472; December, 1945. 

(2) Frank G. Back, "Zoom lens for motion picture cameras with single-barrel 
linear movement," /. Soc. Mot. Pict. Eng., vol. 47, pp. 464^69; December, 1946. 

(3) Frank G. Back, "The physical properties and the practical application of 
the Zoomar lens," J. Soc. Mot. Pict. Eng., vol. 49, pp. 57-64; July, 1947. 

DISCUSSION 

DR. K. PESTRECOV: What is the speed of the lens? 

DR. FRANK G. BACK: The geometrical speed of the lens is//4.5. 

DR. PESTRECOV: Does the speed change while zooming? 

DR. BACK: No. The speed is independent of the zoom. If you set your lens 
for a certain speed this speed remains constant over the entire zoom. 

MR. R. E. LEWIS: What is the resolving power of the lens in lines per milli- 
meter? 

DR. BACK : The 35-mm lens has a resolution of approximately forty lines in the 
center and a little less toward the edges. We are working now on increasing this 
resolution. 

CHAIRMAN WILLIAM H. RIVERS: What approximately is the weight of the 
35-mm lens and is there any additional support needed for field use of this lens? 

DR. BACK: The weight of this lens is not more than the weight of one of the 
large telephoto lenses. For instance, if you take a 25-inch telephoto lens it is 
heavier than this one. Just as it is, it weighs approximately 11 pounds, and we 
have found that for general use it is not absolutely necessary to put any support 
underneath. Of course, a support can be used with the lens very easily. 



1948 ZOOMAR LENS 297 

DR. PESTBECOV: What is the range of focal length covered? 

DR. BACK: The range of this particular lens with the telephoto front lens is 
from three and a half inches up to thirteen inches. We are working now on in- 
creasing the range as well as the focal length. If we use the wide-angle front lens 
by exchanging the front lenses the range goes from approximately two inches up 
to seven inches. 

MR. WILLARD W. JONES: What is the depth of field? 

DR. BACK: The depth of field is exactly the same as on any other lens of com- 
parative focal length. For instance, if you take the lens in the telephoto position 
the depth of field becomes rather shallow as it would be, for instance, on a thirteen- 
inch lens at//4.5. If the zoom lever is in the wide-angle position the depth of field 
increases accordingly. In this case you would have the same depth of field as a 
lens of three and a half inches focal length at//4.5. 

This is the reason why it is not necessary to refocus on those follow shots where 
the subject moves toward or away from the camera and still remains the same size 
on the screen. These follow shots have been focused in the telephoto position 
where the subject is at the greatest distance from the camera because in this posi- 
tion the depth of field is very small. If everything is sharp in this position even 
when the subject comes closer and we go into our wide-angle position by moving 
the zoom lever everything still remains in focus, due to the greater depth of field 
in this position. 

FORTY YEARS AGO 

Moving Pictures from a Balloon 

Berlin, April 25. Photographs for the cinematograph have just been 
taken from a balloon successfully by Herr Ernemann, a Dresden engi- 
neer. As the exciting aerial voyage was ending he passed over the 
Sensteberg coal mine. Here, too, Ernemann succeeded in taking fine 
photographs. But just then the balloon shot down so suddenly that 
even the cinematograph apparatus had to be thrown from the basket. 
Luckily the pictures were afterward found intact. New York World. 

The Moving Picture World, May 2, 1908 



Parabolic Sound Concentrators 



BY R. C. COILE 
WASHINGTON, D. C. 



Summary Parabolic sound concentrators have long been investigated 
for application to military antiaircraft location, radio broadcasting, and 
motion picture recording. Olson and Wolff, of the Radio Corporation of 
America, developed a combination horn-reflector concentrator in 1929. 
Obata and Yosida, of Tokyo University, published measurements of ampli- 
fication in 1930. Hanson, of the National Broadcasting Company, described 
the use of parabolic reflectors in broadcasting in 1931. Dreher reported 
in 1931 on the use of microphone concentrators in motion picture produc- 
tion. Sato and Sasao published the results of tests on the sound fields of 
deep parabolic reflectors in 1932. 

Rocard published an analysis of the theory of the amplification of the 
reflector-type parabola in 1932. Schneider of the Moscow Radio Center 
made amplification and directivity measurements in 1935 while studying 
the application of parabolic concentrators to Russian broadcasting and 
checked his amplification data with Rocard's theory. Gutin, in Leningrad, 
independently derived the theory of amplification and went on to analyze 
directivity in 1935. 

This paper presents the pertinent historical background and reports on 
an experimental verification of the theoretical acoustical directivity of 
parabolic concentrators as well as further checks of the amplification theory. 
The sound fields inside parabolic reflectors have also been investigated 
experimentally with an agreement found with theoretical fields calculated 
by principles of geometrical optics. 



HISTORICAL BACKGROUND 

THE IDEA OF USING a parabolic mirror as a concentrator of sound 
by placing one's ear or a microphone at the,focus was a subject of 
research in World War I. Waetzmann 1 has described German parab- 
olas and Tucker 2 has reported on English and French development 
of plaster and concrete parabolic reflectors. The only quantitative 
data given in these reports is an estimate by Waetzmann that for a 
parabola having an opening diameter of 3.2 meters and a depth of 0.8 
meter the magnification was about five times compared with unaided 
ears for whispers and less for lower notes. 

The first quantitative work published on sound concentrators was a 
report by Olson and Wolff 3 in 1929 of their development of a combi- 
nation horn and reflector. The theory behind this was that the 
amplification of a reflector-type sound concentrator depends on the 
298 SEPTEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 



PARABOLIC SOUND CONCENTRATORS 299 

wavelength of the impinging sound being less than the dimensions 
of the reflector. Hence the low frequencies whose wavelengths are 
larger than the dimensions are amplified very little. But by build- 
ing a horn on the parabolic reflector, the amplification of the horn 
raised the low-frequency response. This design worked fairly well 
and microphone concentrators of this type have been used in Holly- 
wood for recording motion pictures. 

Obata and Yosida, 4 engineers of the Tokyo Imperial University's 
Aeronautical Research Institute, made a'study of acoustical proper- 
ties of some sound collectors for the aircraft sound locator in 
1930. They made measurements of the amplification and directivity 
of two different horns and two 200-centimeter diameter open-bowl 
parabolic reflectors of different focal distance. 

Dreher 5 reported on the use of microphone concentrators in 
motion picture production in this JOURNAL in 1931. Military 
searchlights with a microphone at the focus were used in outdoor re- 
cording, and other types of parabolic bowls were also used. 

The developments of the National Broadcasting Company were 

announced in 1931 by Hanson, 6 chief engineer. Measurements of the 

; amplification, directivity, and effect of microphone position on the 

' axis were reported on a design of an open-bowl parabolic reflector built 

by NBC engineers. 

Engineers of the Aeronautical Research Institute, Sato, Sasao, 
Kubo, and Nisiyama published several papers 7 ' 8 on the sound fields 
i of parabolas in 1932. Their measurements were performed on deep 
parabolic reflectors and hence the results are rather complicated look- 
ing. The measurements were taken in the region beyond the focus, 
for the most part. These writers did not explain these results but 
merely said, "The experiment was very laborious and troublesome 
and therefore was carried out with only two pitches of sound, C 2 and 
C 4 . . . . For C 4 , the sound field becomes very complex and many 
maxima and minima due to interference fill up the space in front of 
the mirror." 

In 1932, the first theoretical treatment was published in Rocard's 
paper 9 on "Les Paraboloides Acoustique" in the Revue d'Acoustique, 
where Rocard derived an expression for the amplification of a para- 
bolic reflector. 

In 1935, Rocard 's theoretical predictions were experimentally veri- 
fied by Schneider, 10 an engineer of the Moscow Radio Center. 
Schneider's paper in the Zhurnal Teknicheskoi Fiziki examined all 



300 COILE September 

previously published work and reported on measurements of am- 
plification which checked Rocard's predictions. 

Neither Rocard nor Schneider had been able to cope with the 
theory of the directivity of a parabolic reflector. In 1935, Gutin, 11 a 
physicist in Leningrad, knowing nothing of the work of either Rocard 
or Schneider, derived independently the expression for amplification 
and went on to work out the theory of directivity which he published 
in the Izvestia Elektropromishlennosti Slabova Toka. 

EXPERIMENTAL STUDY OF PARABOLIC CONCENTRATORS 

An experimental study has been made of the following characteris- 
tics of the parabolic reflector: (1) frequency response, (2) amplifica- 
tion, (3) directivity, and (4) sound fields. The published experimen- 
tal work on reflector-type concentrators has been very meager as out- 
lined above. Most of the published papers show the results of experi- 
ments completed prior to 1932. The microphones used were not 
always of the highest quality or of small size a desirable feature of a 
sound-field measuring device. Some of the work by Obata and 
Yosida, 4 for example, was done using a large homemade condensei 
microphone with most of the experimental work performed indoors 
with the sound source rather close to the parabola. What work had 
been done outside is open to considerable question because of groum 
effects, as the parabola was simply placed upright about a foot off the 
ground. 

Other experimenters have used parabolas with opening diameters 
ranging from 40 to 300 centimeters. A 130-centimeter copper para- 
bolic reflector was used in this experimental setup to simplify measure- 
ment of the sound fields inside the reflector for we might expect acous 
tical reflection similar to optical reflection when the sound wave- 
lengths are small compared to the dimensions of the parabola am 
diffraction effects when the wavelengths are comparable to the dimen- 
sions. The large size of the parabola indicated outdoor measurements 
to avoid errors from reflected sound although outdoor measurements 
present difficulties of wind and extraneous noises. 

Kellogg 12 described five methods for minimizing echo errors in & 
paper in the Journal of the Acoustical Society some years ago. Fig. 1 
depicts these schemes. In A both the loudspeaker and the microph* >i i < 
are well above the ground. If the distance is large compared with 
the wavelength of the lowest frequency employed the image sourcea 



1948 



PARABOLIC SOUND CONCENTRATORS 



301 



are negligible. In B image sources are taken into consideration by 
placing both the loudspeaker and the microphone on the ground 

i so that the difference between path length r from loudspeaker to 

I microphone and the path length r' from image to microphone is less 
than a quarter wavelength of the sound. In C the speaker is sup- 
ported in the air with the microphone on the ground. The sound re- 
flected from the ground, if the ground is not a good absorbent, is some- 
times strong enough to cause some back pressure on the loudspeaker. 
This can be fixed by putting the microphone on a slope as shown in D, 
so that the sound is reflected off at such an angle that it has little 

i effect on the loudspeaker. 

I One more method is to get 

j the microphone out on a 

| boom as far from any build- 

[ing as possible and to have 

I the sound source at the cor- 

j ner of the building as illus- 
trated in E. 
The most convenient 

j method for this particular 



LOUDSPEAKER AND 
MICROPHONE WELL 
ABOVE GROUND 



TAKING ACCOUNT 
OF IMAGE 



MICBOPHONE ON 
GROUND 



REACTION OF ECHO 
ON SPEAKER. AVOIDED 




WORKING AT COR.NER. OF BUILDING 

Fig. 1 Arrangements for minimizing echo 
errors. 



I experimental setup was a 
i variation of D as illustrated 

in Fig. 2. The sound source 
[was a General Radio beat- 
I frequency oscillator which 
| excited a Western Electric 
| loudspeaker unit in a 6-foot 

exponential horn suspended 

out of a window of one of 
j the sound laboratories at the Massachusetts Institute of Technology. 
j The parabolic reflector was placed about 100 feet from the side of the 
! building and was pointed toward the sound source. A Western 

Electric Type 630-A moving-coil microphone, step-up transformer, 

General Radio amplifiers, and General Radio output meter were 
! used in the frequency response-amplification measurements, and a 

General Radio sound-level meter with a Brush sound-cell crystal 

microphone for sound-field measurements. 

FREQUENCY RESPONSE- AMPLIFICATION 
An expression for the theoretical frequency response and 



302 



COILE 



September 



amplification of parabolic reflectors was derived independently by 
Rocard and Gutin. This expression is as follows : 



I = depth of parabola 
R = radius of opening 



3 RD FLOOR. WINDOW OF THE 
SOUND LABORATORY 




where 

P/s = pressure with concentrator 
Pa = pressure without concentrator 

a = focal distance 

For the parabola under test, 
R the radius of opening was 
65 centimeters; a the focal 
distance was 30 centimeters; 
and I the depth was 35 centi- 
meters. The expression for 
the amplification of this pa- 
rabola reduces to 



Fig. 2 Experimental setup. 

Equipment: 1. Parabolic bowl reflec- 
tor: diameter, 130 centimeters; depth, 35 
centimeters; focal distance, 30 centimeters. 

2. Microphone, Western Electric 630- 
A moving-coil microphone. 

3. Step-up transformer, 30 to 100,000 
ohms. 

4. General Radio battery-operated 
amplifier. 

5. Step-down transformer. 

6. Transmission line. 

7. Step-up transformer, 30 to 100,000 
ohms. 

8. General Radio battery-operated 
amplifier. 

9. General Radio output-level meter. 

10. General Radio beat-frequency oscil- 
lator, 20 to 20,000 cycles per second. 

11. Six-foot exponential horn with 
Western Electric 555 unit. 

12. General Radio sound-level meter 
with Brush crystal microphone. 



This theoretical amplification 
at the focus is an inverse func- 
tion of the wavelength and is 
plotted as the straight line in 
Fig. 3. 

The frequency response and 
amplification of the parabolic 
concentrator were determined 
first by measuring the response 
of the microphone alone in free 
space, and then measuring the 
response of the microphone in 
the concentrator. The micro- 
phone was placed at the focus 
of the paraboloid. The meas- 
ured frequency response and 
amplification characteristic are! 
shown in Fig. 3. This agreement between measured gain of the con- 
centrator and the computed values of amplification is as good as that j 
reported by Gutin, 11 for the work of Obata and Yosida, 4 and the 
comparisons reported by Schneider. 10 The measured amplification j 
differs from the computed amplification by about 10 decibels at the 



1948 



PAKABOLIC SOUND CONCENTRATORS 



303 



higher frequencies (7000 cycles) for the parabola investigated. 
Obata and Yosida's 4 measurements for frequencies from 475 to 188 
cycles show the same trend, a divergence between theory and meas- 
urement for the higher frequencies. At their highest frequency of 
475 cycles, the difference between theoretical and measured amplifica- 
tion was on the order of 20 per cent for one parabola 200 centimeters 
in diameter and 72.5 centimeters in focal length; and about 80 per 
cent difference for another parabola of the same diameter with a 54.5 



40 

335 
UJ 
cfl 

S 30 
Q 

225 

_1 
LJ20 
> 
U 

J .5 
1- 

|,0 

g 5 


2( 










^X 




COMPUT 

(J.) , 


ED AMPLIFICATION 
4TT 0, ^ Cl+R 2 ) 


^x 






v Rc 


A ' 4a l y 

/ 


/ 








/ 










/ / 








^x 


*^~ AMPLIFICATION CP 


CONCENT!^ 


ATOR. 


/ 


x^^ 


D=I3O cm, f -io 
(e=65CYn a = 


Cm, d-35 
30cm) 


CWl 


,/X 










7^' ' ~ 










)0 ' 500 1000 MOO 10000 



IN CpS 

Fig. 3 Frequency-response amplification of the parabolic 
sound concentrator. 



centimeter focal length. The curves of Schneider show this same 
trend. Schneider does not draw theoretical curves for frequencies 
higher than 4000 cycles because the disagreement is so large. 

The size of the probe microphone used in the measurements affects 
the accuracy of the results. Schneider used three microphones in his 
tests, a large Reisz (carbon) with a diaphragm area of 70 square centi- 
meters, a small Reisz with a diaphragm area of 40 square centimeters, 
and a condenser microphone with an area of 20 square centimeters. 
Examination of his data shows that the smaller the diaphragm area, 
the better the agreement between theoretical and measured results. 
Schneider did not attempt to explain this phenomenon. It may 
possibly be attributed to phase-cancellation effects, the diaphragm 
being so large that the higher-frequency sounds which behave more or 
less as geometrical optics predict, arriving in pencils of rays, hit the 
diaphragm in different phase thus reducing the output. Instead of 



304 COILE September 

having an infinitely small collector of the sound arriving at the focus in 
phase, we have a large sound-receiving surface that can pick up sound 
of different phase which will tend to reduce the output. The Western 
Electric Type 630-A microphone used in the frequency response-am- 
plification tests has a diaphragm area estimated at 10 square centi- 
meters, and the Brush sound-cell crystal used as a probe microphone 
in tracing out the sound fields has an area estimated at 2.5 square 
centimeters. 

DIRECTIVITY 

The directivity characteristic is important in many applications of 
the parabolic reflector. Sato and Sasao have published experimental 
directivity curves and Schneider published some curves. The first 
published paper on an analysis of the theory of the directivity of the 
parabolic reflector is that of Gutin, who derived an expression for the 
coefficient of amplification at the focus of a paraboloid for an arriving 
sound wave whose normal made an angle a with the axis as follows 



/ 
JO 



O 1 + 

R 






,_ , 



Gutin derived a simpler expression using the theorem of reciprocity 
that is essentially the same at higher frequencies. This expression for 
the coefficient of amplification at the focus is 



Neglecting the incoming wave with respect to the reflected wave, 
the directivity characteristic expressed as a fraction of the maximum 
amplification (i.e., a = 0) is 



.R 

f2a h(2akt siii ) 

Jo 






(I + t 2 ) In (1 - 

Gutin has given a table showing the position of the first minimum of, 
the directivity for values of R/2a. 

The measured directivity characteristic is shown in Fig. 4. The 
directivity was determined first by lining up the axis of the parabola | 



1948 



PARABOLIC SOUND CONCENTRATORS 

TABLE I 
FIRST MINIMUM OF DIRECTIVITY 



R/2a 



sin a 



1.0 


0.683X/# 


0.7 


0.66 \/R 


0.6 


0.64 \/R 


0.4 


0.62 \/R 





0.61 X/fl 



305 




150' 



Fig. 4 Directivity characteristics: Massachusetts 
Institute of Technology parabolic concentrator. 



with the axis of the 6-foot exponential-horn sound source, and then 
tilting the parabola and measuring the response at different angles. 
The lobes other than the fundamental were negligible and could not 
be distinguished from background noise. The main features of in- 
terest are the angles at which the response falls to its first minimum. 
These angles can be calculated by the method developed by Gutin. 
The procedure is as follows : The angle at which the directional char- 
acteristic goes through its first minimum is given by the expression 

a = sm~ 1 K \/R 

Where X = wavelength of sound being received 

R = radius of opening of parabola 
K = constant depending on 72/2a (see Table I). 



306 COILE September 

The constant K is determined by calculation of R/2a and then use of 
Table I. For the parabola investigated R = 65 centimeters; a = 30 
centimeters; R/2a = 1.08; K = 0.69. Hence we can compute the 
angle of the first minimum. 

TABLE II 
CHECK OF THEORY AND MEASUREMENTS OF DIRECTIVITY 



/ 


500 cycles 


2000 cycles 


5000 cycles 


X 


69 centimeters 


17.2 centimeters 


6.9 centimeters 


\/R 


1.06 


0.264 


0.106 


0.69 \/R 


0.725 


0.180 


0.0725 


a (computed) 


46 . 5 degrees 


10. 2 degrees 


4 . 2 degrees 


a (measured) 


45 degrees 


15 degrees 


5 degrees 



This agreement of theoretical and measured angles for the first 
minimum was a reasonably good check of Gutin's directivity theory. 
It is of interest to note that the Izvestia Elektropromishlennosti 
Slabovo Toka is available at so few libraries in the world that even 
Schneider, another Russian, publishing his paper in the Zhurnal Tek- 
nicheskoi Fiziki, also in 1935, stated "The story of the concentrator 
is very complicated. The amplification has an approximate solu- 
tion. . . . The directivity characteristics are without theory. ..." 

The experimental directivity curves of Schneider measured with a 
condenser microphone have also been compared with theoretical pre- 
dictions. The calculations have been carried through in a manner 
similar to those for the 'parabola at the Massachusetts Institute of 
Technology: R = 47 centimeters; a = 27 A centimeters; R/2a = 
0.86; K = 0.675. 

TABLE III 
DIRECTIVITY CHECK OF SCHNEIDER'S DATA 

/ 700 cycles 1600 cycles 3000 cycles 5500 cycles 

X 49.2 centi- 21.5 centi- 11.4 centi- 6.25 centi- 
meters meters meters meters 

\/R 1.04 0.456 0.242 0.133 

0.675 \/R 0.705- 0.308 0.163 0.0896 

a (computed) 45 degrees 18 degrees 9. 4 degrees 5. 2 degrees 

a (measured) 50 degrees 42 degrees 11 degrees 5 degrees 



The results check reasonably well .with the exception of the 1600- 
cycle data. However, Schneider's measurements were made indoorsi 



1948 



PARABOLIC SOUND CONCENTRATORS 



307 



so that there is a greater possiblity for a freak measurement than if the 
measurements had been made outside with less chance of reflections 
introducing errors. 

SOUND FIELDS 

There has been very little published on the sound fields of parabolic 
reflectors. Sato and Sasao 8 have reported measurements on fields in 
a deep parabola. These previous experiments studied complex sound 
fields in regions beyond the focus. It was thought of interest to ex- 
amine the region between the focus and the vertex. 




DIRECTRIX. B 

Fig. 5 Reflection from a parabolic mirror.* 

* Wood, R. W.: "Physical Optics," Macrnillan Company, New York, N. Y., 
1934, p. 47. 

According to the principles of geometrical optics a source placed at 
the focus emitting spherical waves will have them reflected at the 
walls of the parabola and sent out as plane wave fronts. And, con- 
versely, plane waves arriving at the parabola will be reflected as 
spherical waves converging on the focus. When the incident and re- 
flected waves meet there can be either constructive or destructive in- 
terference. If the difference in path length is m A, where m = 0, 1, 2, 
3, 4, ... there will be constructive interference. If the difference in 
path Itngth is (2m + 1) (A/2) where m = 0, 1, 2, 3, 4, . . .there will be 
destructive interference. 

Hence, in attacking this portion of the problem, the contours of 
constructive and destructive interference were first determined by 



COILE 



September 



geometrical optical construction and then measured by the acous- 
tical setup described. 

The construction of the reflected wave fronts is a simple matter. 
The fundamental definition of a parabola is that it is the locus of 
points equidistant from a fixed line called the directrix and a point 
called the focus. Reflected wave fronts may be constructed in a 
graphical manner similar to that outlined by Wood. 13 

In Fig. 5 let be the focus of the parabola and line BD the direc- 
trix. Let the unreflected wave front be represented by line HG. 



+ MAXIMA- POINTS OF CONSTRUCTIVE INTERFERENCE 
- MINIMA-POINTS OF DESTRUCTIVE INTERFERENCE 



UNCEFLECTED 
WAVE FRONTS 



REFLECTED 
WAVE FRONTS 




CONTOURS 
OF MAXIMA' 



CONTOURjS 
OF MINIMA^ 



Fig. 6 Calculation of sound-field contours by 

geometric optical interference phenomena. 
/ = 1720 cycles per second 
X = 20 centimeters 

Through any two points on the parabola A and C draw lines from 0, 
the focus. Construct circles about points A and C of radius equal to 
the distance from these points on the parabola to the unreflected wave 
front. A circle drawn about with radius OE will pass through point 
F and will be the reflected wave front. This may be proved as fol- 
lows : every point on the parabola is equidistant from focus and di- 
rectrix, OA = AB and OC = CD; the small circles constructed about 
A and C had radii of AE = AH and CG = CF; but now OE = BH 
and OF DG adding the two parts of each line. But since DG = BH, 
for the unreflected wave front is parallel to the directrix, hence OE = 



1948 



PARABOLIC SOUND CONCENTRATORS 



309 



OF and a circle of the reflected wave front has been determined. 
Now we can see that as the unreflected wave front moves into 
the parabola, the reflected wave fronts become smaller and smaller 
circles converging on the focus. 



SCALE : I cm = 5 cm. 




COMPUTED 
CONTOURS OF 

MAXIMA. 



MEASURED POINTS 
OF MAXIMA 



FOCUS 

PARABOLIC BOWL 

BEFLECTOB. 
DIAMETER. 13O Cm 
DEPTH 35 cm 
FOGAL DISTANCE 
30 Cin 



^. MEASURED POINTS 
OF MINIMA 



COMPUTED 
^CONTOUR.6 
OF MINIMA 



Fig. 7 Sound-field contpurs^off constructive and 
t A ** destructive interference. 

/ = 3440 cycles per second 

X = 10 centimeters 

Brush sound-cell microphone; Federal Radio 
sound-level meter. 

A useful short cut in drawing these wave fronts is apparent on ex- 
amination. The reflected wave fronts, circles about the focus, inter- 
sect the parabola at the same points as the unreflected plane wave 
front. Therefore, it is an easy matter to draw a circle with center at 
the focus and radius equal to the distance from the focus to the points 
of intersection of the parabola and the plane wave front. 



310 COILE September 

Using this simple method of constructing reflected wave fronts, the 
contours of points of constructive interference (maxima) and points of 
destructive interference (minima) may be traced out after finding 
these points by checking path lengths. This construction is illus- 
trated in Fig. 6. A series of plane unreflected wave fronts approach- 
ing the parabola has been drawn spaced a half wavelength apart. 
The frequency of 1720 cycles per second has been chosen to give a con- 
venient wavelength of 20 centimeters (X = c/f = 34400/1720). A 
series of concentric circles converging on the focus has been drawn 
corresponding to the c/f approaching plane wave fronts. There are 
numerous points of intersection. For each of these points we trace 
out the difference in path length between the incident and reflected 
wave. For example, at the surface of the parabola the path-length 
difference is zero, hence constructive interference; but moving out 
from the parabola along any circle of a reflected wave front there are 
points whose path-length difference is X/2 designated by a minus 
sign; X designated as plus, 3X/2 minus, etc. The points of construc- 
tive interference marked "plus" have been joined and in a similar 
fashion lines have been drawn through the "minus" points. These 
lines are the contours of maxima and minima. 

These contours were traced out by a crystal probe microphone and 
a General Radio sound-level meter. Predicted and measured data 
have been plotted in Fig. 7. Examination of the figure shows the 
theoretical contours of constructive interference plotted as solid lines 
in the upper half of the parabola and the theoretical contours of de- 
structive interference plotted as' dotted lines in the lower half. Of 
course, both contours occur in three dimensions as a series of confocal 
shells of paraboloids of revolution, but for our purposes the contours 
are cross-section pictures of the parabola with the contours of minima 
made invisible in the upper half and the contours of maxima made in- 
visible in the lower half. 

The experimental points have been plotted as little circles for 
maxima and X's for minima. There are two places where the points 
do not check so well, points a great distance from the axis, and points 
on the axis. The explanation for the discrepancy of the points quite 
distant from the axis may be attributed to two things : distortion of 
the sound field by ground effects, and/or lack of rigidity of the 
microphone probe equipment. Measurements could not be made with 
sufficient precision to determine quantitatively the magnitude of the 
ground effect. For the purpose of checking the theoretical contours 



1948 PARABOLIC SOUND CONCENTRATORS 311 

of constructive and destructive interference the experimental points 
nearer the axis must suffice and it is felt that, on the whole, a reasonable 
agreement is found within the magnitude of the errors of measurement. 

REFERENCES 

(1) E. Waetzmann, "Parabolic reflectors" (In German), Zeit.filr Tech. Phys., 
vol. 2, p. 191; 1921. 

(2) W. S. Tucker, "Sound reception," Royal Aero. Soc. Proc., vol. 28, p. 504; 
1924. 

(3) H. F. Olson and I. Wolff, "Sound concentrator for microphones," J. 
Aeons. Soc. Amer., vol. 1, pp. 410-417; March, 1929. 

(4) Juichi Obata and Yekio Yosida, "Acoustical properties of some sound 
collectors for the aircraft sound locator" (In English), Aero. Res. Inst., Tokyo Im- 
perial University, vol. 5, pp. 231-249; July, 1930. 

(5) Carl Dreher, "Microphone concentrators in picture production," J. Soc. 
Mot. Pict. Eng., vol. 16, pp. 23-31 ; January, 1931. 

(6) O. B. Hanson, "Microphone technique in broadcasting," J. Acous. Soc. 
Amer., vol. 3, pp. 81-93; 1931. 

(7) Kozi Sato, Masaki Sasao, Keiiti Kubo, and Masao Nisiyama, "On the 
acoustical properties of parabolic reflectors" (In Japanese), Aero. Res. Inst., 
Tokyo Imperial University, vol. 8, pp. 18-64; 1932; pp. 339-356; 1933. 

(8) Kozi Sato and Masaki Sasao, "On the sound field of parabolic reflectors" 
(In English), Proc.*Physics-Math. Soc. (Japan), vol. 14, pp. 363-372; 1932. 

(9) M. Y. Rocard, "Les paraboloides acoustique" (In French), Rev. d'Acous- 
tique, vol. 1, pp. 222-231 ; 1932. 

(10) J. I. Schneider, "A microphone concentrator" (In Russian), Zhurnal Tek- 
nicheskoi Fiziki (Jour. Tech. Phys.}, vol. 5, pp. 855-867; 1935. 

(11) L. J. Gutin, "On the theory of the parabolic sound reflector" (In Russian), 
Izvestia Elektropromishlennosti Slabovo Toka (Leningrad), vol. 9, pp. 9-25, 75-76; 
1935. 

(12) E. W. Kellogg, "Loud speaker sound pressure measurements," /. Acous. 
Soc. Amer., vol. 2, p. 157; 1930. 



Committees of the Society 

(CORRECT TO AUGUST 10, 1948) 

ADMISSIONS 

To pass upon all applications for membership, applications for transfer, 
and to review the Student and Associate membership list periodically 
for possible transfer to the Associate and Active grades, respectively. 
The duties of each committee are limited to applications and transfers 
originating in the geographic area covered. 

D. B. JOT, Chairman, East 

30 E. 42d St. 
New York 17, N. Y. 

E. A. BERTRAM JAMES FRANK, JR. G. T. LORANCE 

M. R. BOYER L. E. JONES PIERRE MERTZ 

HERBERT GRIFFIN, Chairman, West 

133 E. Santa Anita Ave. 

Bui-bank, Calif. 

J. W. BOYLE P. E. BRIGANDI H. W. MOYSE 

C. R. DAILY 


BOARD OF EDITORS 

To pass upon the suitability of all material submitted for publication, or 
for presentation at conventions, and publish the JOURNAL. 

A. C. DOWNES, Chairman 
2181 Niagara Dr. 
Lakewood 7, Ohio 

A. W. COOK C. W. HANDLEY P. J. LARSEN 

J. G. FRAYNE A. C. HARDY G. E. MATTHEWS} 

A. M. GUNDELFINGER PlERRE MERTZ 

CINEMATOGRAPHY 

To make recommendations and prepare specifications for the operation, 
maintenance, and servicing of motion picture cameras, accessory equip- 
ment, studio and outdoor set lighting arrangements, camera technique, 
and the varied uses of motion picture negative films for general photog- 
raphy. 

C. G. CLARKE, Chairman 
328 S. Bedford Dr. 
Beverly Hills, Calif. 

J. W. BOYLE ARTHUR MILLER ARTHUR REEVES 

KARL FREUND JOSEPH RUTTENBERGI 

312 SEPTEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 



COMMITTEES OF THE SOCIETY 313 

COLOR 

To make recommendations and prepare specifications for the operation, 
maintenance, and servicing of color motion picture processes, accessory 
equipment, studio lighting, selection of studio set colors, color cameras, 
color motion picture films, and general color photography. 

HERMAN H. DUEBR, Chairman 

Ansco 
Binghamton, N. Y. 

J. A. BALL L. E. CLARK J. G. FRAYNE 

R. H. BINGHAM R. O. DREW L. T. GOLDSMITH 

M. R. BOYER ALBERT DURYEA A. M. GUNDELFINGER 

H. E. BRAGG R. M. EVANS A. J. MILLER 

0. 0. CECCARINI G. F. RACKETT 

CONVENTION 

To assist the Convention Vice-President in the responsibilities pertain- 
ing to arrangements and details of the Society's technical conventions. 

W. C. KTJNZMANN, Chairman 

Box 6087 
Cleveland 1, Ohio 

JAMES FRANK, JR. H. F. HEIDEGGER A. SHAPIRO 

E. R. GEIB O. F. NEU L. H. WALTERS 

EXCHANGE PRACTICE 

To make recommendations and prepare specifications on the engineer- 
ing or technical methods and equipment that contribute to efficiency in 
handling and storage of motion picture prints, so far as can be obtained 
by proper design, construction, and operation of film-handling equip- 
ment, air-conditioning systems, and exchange office buildings. 
(Under Organization) 

FELLOW AWARD 

To consider qualifications of Active members as candidates for elevation 
to Fellow, and to submit such nominations to the Board of Governors. 

D. E. HYNDMAN, Chairman 

342 Madison Ave. 

New York 17, N. Y. 

E. A. BERTRAM W. C. KTTNZMANN . L. L. RYDER 

M. R. BOYER G. T. LORANCE A. SHAPIRO 

JAMES FRANK, JR. J. A. MATJRER E. I. SPONABLE 

C. R. KEITH W. V. WOLFE 



314 



COMMITTEES OF THE SOCIETY 



September 



FILM DIMENSIONS 

To make recommendations and prepare specifications on those film 
dimensions which affect performance and interchangeability, and to 
investigate new methods of cutting and perforating motion picture film 
in addition to the study of its physical properties. 

(Under Organization) 

FILM-PROJECTION PRACTICE 

To make recommendations and prepare specifications for the operation, 
maintenance, and servicing of motion picture projection equipment, pro- 
jection rooms, film-storage facilities, stage arrangement, screen dimen- 
sions and placement, and maintenance of loudspeakers to improve the 
quality of reproduced sound and the quality of the projected picture in the 
theater. 

(Under Organization) 

HIGH-SPEED PHOTOGRAPHY 

To make recommendations and prepare specifications for the con- 
struction, installation, operation, and servicing of equipment for photo- 
graphing and projecting pictures taken at high repetition rates or with 
extremely short exposure times. 

JOHN H. WADDELL, Chairman 

463 West St. 
New York 14, N. Y. 

R. E. FARNHAM 
COMMANDER FRAZER 
H. M. LESTER* 
L. MARTIN 

J. J. McDEVITT 



E. ANDRES 
K. M. BAIRD 
M. BEARD 
B. BRIXNER 
HAROLD EDGERTON 
MAJOR ELLIOTT 



A. NEYHART 
BRIAN O'BRIEN 
EDWARD SCHMIDT 
C. SLACK 
M. L. SANDELL 
E. W. WIGHTMAN** 



* Representing Photographic Society of America. 
** Representing Photographic Engineering Society. 



HISTORICAL AND MUSEUM 

To collect facts and assemble data relating to the historical development 
of the motion picture industry to encourage pioneers to place their work 
on record in the form of papers for publication in the JOURNAL, and to 
place in suitable depositories equipment pertaining to the indus- 
try. 

(Under Organization) 

HONORARY MEMBERSHIP 

To search diligently for candidates who through their basic inventions or 
outstanding accomplishments have contributed to the advancement of 
the motion picture industry and are thus worthy of becoming Honorary 
members of the Society. 



1948 COMMITTEES OF THE SOCIETY 315 

HONORARY MEMBERSHIP (continued) 

H. W. REMERSCHEID, Chairman 

716 N. La Brea Ave. 

Hollywood, Calif. 

F. E. CAHILL, JR. C. W. HANDLEY 

WALTER CLARK REEVE O. STROCK 

JOURNAL AWARD 

To recommend to the Board of Governors the author or authors of the 
most outstanding paper originally published in the JOURNAL during the 
preceding calendar year to receive the Society's JOURNAL Award. 

J. I. CRABTREE, Chairman 

Eastman Kodak Company 

Rochester 4, N. Y. 

C. R. DAILY R. E. LEWIS 

L. T. GOLDSMITH D. R. WHITE 

LABORATORY PRACTICE 

To make recommendations and prepare specifications for the operation, 
maintenance, and servicing of motion picture printers, processing ma- 
chines, inspection projectors, splicing machines, film-cleaning and treat- 
ing equipment, rewinding equipment, any type of film-handling acces- 
sories, methods, and processes which offer increased efficiency and im- 
provements in the photographic quality of the final print. 

(Under Organization) 

A. A. DURYEA, Chairman 
90 W. Horton St. 
City Island, N. Y. 



MEMBERSHIP AND SUBSCRIPTION 

To solicit new members, obtain nonmember subscriptions for the JOUR- 
NAL, and to arouse general interest in the activities of the Society and its 
publications. 

L. E. JONES, Chairman, East 

427 W. 42d St. 
New York 18, N. Y. 

Atlantic Coast 

BERTIL CARLSON C. F. HORSTMAN C. W. SEAGER 

A. R. GALLO W. C. KUNZMANN A. G. SMITH 

T. J. GASKI O. F. NEU C. M. WEBER 

N. D. GOLDEN P. D. RIES C. R. WOOD, SR. 



316 COMMITTEES OF THE SOCIETY 

MEMBERSHIP AND SUBSCRIPTION 

H. H. WILSON, Chairman, Midwest 

240 E. Ontario St. 

Chicago, 111. 

JOHN POWERS 

T. I. RBSS 

JOHN SPINNEWEBER 



B. W. DsPEU 
R. E. FARNHAM 

C. E. HEPPEBERGER 



September 
(continued) 



LLOYD THOMPSON 
ELMER VOLTZ 
JOHN ZUBER 



G. C. MISENER, Chairman, Pacific Coast 

6424 Santa Monica Blvd. 

Hollywood 38, Calif. 

L. W. CHASE, JR. L. T. GOLDSMITH W. A. MUELLER 

J. P. CORCORAN HERBERT GRIFFIN G. E. SAWYER 

C. R. DAILY EMERY HUSE W. L. THAYER 

J. G. FRAYNE K. F. MORGAN W. V. WOLFE 

H. W. MOYSE 

16-Mm 

G. A. CHAMBERS C. L. LOOTENS A. G. PETRASEK 

A. W. COOK L. R. MARTIN F. B. ROGERS 

R. C. HOLSLAG W. H. OFFENHAUSER, JR. R. J. SHERRY 

W. F. KRUSE LLOYD THOMPSON 

Foreign 

R. J. ENGLER B. J. KROGER H. S. WALKER 

R. O. STROCK 

Television 

R. B. AUSTRIAN, Chairman 

247 Park Ave. 
New York 17, N. Y. 



NOMINATIONS 

To recommend nominations to the Board of Governors for annual elec- 
tion of officers and governors. 

E. A. WILLIFORD, Chairman 

40 Charles St. 
Binghamton, N. Y. 



JAMES FRANK, JR. 
L. T. GOLDSMITH 
J. K. MILLIARD 



EMERY HUSE 
E. W. KELLOGG 



P. J. LARSEN 
K. F. MORGAN 
M. G. TOWNSLEY 



1948 COMMITTEES OF THE SOCIETY 317 

PAPERS 

To solicit papers and provide the program for semiannual conventions, 
and make available to local sections for their meetings papers pre- 
sented at national conventions. 

G. A. CHAMBERS, Chairman 

343 State St. 
Rochester 4, N. Y. 

JOSEPH E. AIKEN, Vice-Chairman R. T. VAN NIMAN, Vice-Chairman 

225 Orange St., S. E. 4331 W. Lake St. 

Washington 20, D. C. Chicago 24, 111. 

E. S. SEELEY, V T ice-Chairman N. L. SIMMONS, Vice- Chairman 

161 Sixth Ave. 6706 Santa Monica Blvd. 

New York 13, N. Y. Hollywood 38, Calif. 

H. S. WALKER, Vice- Chairman 
1620 Notre Dame St., W. 
Montreal, Que., Canada 

G. M. BEST C. R. DAILY G. E. MATTHEWS 

P. E. BRIGANDI A. R. DAVIS J. H. MAYNARD 

J. P. CORCORAN W. P. DUTTON P. A. McGuiRE 

G. R. CRANE J. L. FORREST EDWARD SCHMIDT 

PRESERVATION OF FILM 

To make recommendations and prepare specifications on methods of 
treating and storage of motion picture film for active, archival, and 
permanent record purposes, so far as can be prepared within both the 
economic and historical value of the films. 

CHARLES G. WEBER, Chairman 
National Bureau of Standards 

Washington 25, D. C. 

J, G. BRADLEY J. I. CRABTREE TERRY RAMSAYE 

H. T. COWLING J. L. FORREST V. B. SEASE 

J. E. GIBSON 

PROCESS PHOTOGRAPHY 

To make recommendations and prepare specifications on motion picture 
optical printers, process projectors (background process), matte proc- 
esses, special process lighting technique, special processing machines, 
miniature-set requirements, special-effects devices, and the like, that 
will lead to improvement hi this phase of the production art. 
(Under Organization) 

LIN WOOD DUNN, Chairman 
RKO-Radio Pictures 

780 Gower St., 
Los Angeles 3, Calif. 



318 COMMITTEES OF THE SOCIETY September 

PROGRESS 

To prepare an annual report on progress in the motion picture industry. 
C. R. SAWYER, Chairman 

233 Broadway 
New York 7, N. Y. 

J. E. AIKEN R. E. LEWIS J. W. THATCHER 

C. W. -HANDLEY W. A. MUELLER W. V. WOLFE 

W. L. TESCH 

PROGRESS MEDAL AWARD 

To recommend to the Board of Governors a candidate who by his in- 
ventions, research, or development has contributed in a significant man- 
ner to the advancement of motion picture technology, and is deemed 
worthy of receiving the Progress Medal Award of the Society. 
F. E. CARLSON, Chairman 

Nela Park 
Cleveland 12, Ohio 

HARRY BRAUN R. M. CORBIN 

J. W. BOYLE W. C. MILLER 

PUBLICITY 

To assist the Convention Vice-President in the release of publicity ma- 
terial concerning the Society's semiannual technical conventions. 

*HAROLD DESFOR, Chairman 

RCA Victor Division 
Radio Corporation of America 

Camden, N. J. 

*LEONARD BIDWELL P. A. McGuiRE 

HARRY SHERMAN 

* Advisory Member. 

SCREEN BRIGHTNESS 

To make recommendations, prepare specifications, and test methods 
for determining and standardizing the brightness of the motion picture 
screen image at various parts of the screen, and for special means or 
devices in the projection room adapted to the control or improvement of 
screen brightness. 

E. R. GEIB, Chairman 

Box 6087 
Cleveland 1, Ohio 

HERBERT BARNETT W. W. LOZIER C. W. TUTTLE 

F. E. CARLSON G. M. RENTOTTMIS C. R. UNDERBILL 

ARTHUR HATCH ALLEN STIMSON H. E. WHITE 

W. F. LITTLE A. T. WILLIAMS 



1948 COMMITTEES OP THE SOCIETY 319 

16-MM AND 8-MM MOTION PICTURES 

(Formerly Nontheatrical Equipment) 

To make recommendations and prepare specifications for 16-mm and 8- 
mm cameras, 16-mm sound recorders and sound-recording practices, 
16-mm and 8-mm printers and other film laboratory equipment and 
practices, 16-mm and 8-mm projectors, splicing machines, screen di- 
mensions and placement, loudspeaker output and placement, preview 
or theater arrangements, test films, and the like, which will improve the 
quality of 16-mm and 8-mm motion pictures. 

H. J. HOOD, Chairman 

333 State St. 
Rochester 4, N. Y. 

W. C. BOWEN R. C. HOLSLAG D. A. PBITCHABD 

F. L. BRETHAUER R. KINGSLAKE L. T. SACHTLEBEN 

F. E. BROOKER G. T. LORANCE R. SPOTTISWOOD 

S. L. CHERTOK W. W. LOZIER H. H. STRONG 

E. W. D'ARCY D. F. LYMAN A. L. TERLOUW 

J. W. EVANS W. C. MILLER L. THOMPSON 

C. R. FORDYCE W. H. OFFENHAUSER, JR. M. G. TOWNSLEY 
A. G. PETRASEK 



SOUND 

To make recommendations and prepare specifications for the operation, 
maintenance, and servicing of motion picture film, sound recorders, 
re-recorders, and reproducing equipment, methods of recording sound, 
sound-film processing, and the like, to obtain means of standardizing 
procedures that will result in the production of better uniform quality 
sound hi the theater. 

L. T. GOLDSMITH, Chairman 

Warner Brothers Pictures, Inc. 

Burbank, Calif. 

G. L. DIMMICK, V 'ice-Chairman 

RCA Victor Division 

Camden, N. J. 

A. C. BLANEY L. D. GRIGNON OTTO SANDVIK 

D. J. BLOOMBERG ROBERT HERR G. E. SAWYER 
F. E. CAHILL, JR. J. K. MILLIARD R. R. SCOVILLE 

E. W. D'ARCY L. B. ISAAC W. L. THAYER 
R. J. ENGLER E. W. KELLOGG M. G. TOWNSLEY 
J. G. FRAYNE J. P. LIVADARY R. T. VAN NIMAN 

W. C. MILLER 



320 



COMMITTEES OF THE SOCIETY 



Septembei 



STANDARDS 

To survey constantly all engineering phases of motion picture produc- 
tion, distribution, and exhibition, to make recommendations and pre- 
pare specifications that may become proposals for American Standards. 
This Committee should follow carefully the work of all other commit- 
tees on engineering and may request any committee to investigate and 
prepare a report on the phase of motion picture engineering to which it 
is assigned. . 

F. E. CARLSON, Chairman 

Nela Park 
Cleveland 12, Ohio 



F. S. BERMAN 
CHARLES CLARKE 
H. H. DUERR 
LINWOOD DUNN 
A. A. DURYEA 



F. T. BOWDITCH 
E. K. CARVER 
GORDON EDWARDS 

L. A. JONES 
C. R. KEITH 



Chairmen of Engineering Committees 
E. R. GEIB 
L. T. GOLDSMITH 
M. A. HANKINS 
H. J. HOOD 

M ember s-at'Large 
E. W. KELLOGG 

R. KlNGSLAKE 

Members Ex-OJjicio 
V. O. KNUDSEN 

STUDIO LIGHTING 



D. E. HYNDMAI 
LEONARD SATZ 
JOHN WADDEL 

C. G. WEBER 

D. R. WHITE 



G. T. LORANCE 
D. LYMAN 
OTTO SANDVIK 

GEORGE Nixoi 
F. W. SEARS 



To make recommendations and prepare specifications for the operation, 
maintenance, and servicing of all types of studio and outdoor auxiliary 
lighting equipment, tungsten light and carbon-arc sources, lighting-effect 
devices, diffusers, special light screens, etc., to increase the general en- 
gineering knowledge of the art. 

M. A. HANKINS, Chairman 

937 N. Sycamore Ave. 

Hollywood 38, Calif. 



J. W. BOYLE 

W. E. BLACKBURN 

RICHARD BLOUNT 



KARL FRETJND 
C. W. HANDLEY 



TELEVISION 



C. R. LONG 
W. W. LOZIER 

D. W. PRIDEAI 



To study television art with special reference to the technical interre- 
lationships of the television and motion picture industries, and to make 
recommendations and prepare specifications for equipment, methods, 
and nomenclature designed to meet the special problems encountered at 
the junction of the two industries. 



1948 



COMMITTEES OF THE SOCIETY 



321 



TELEVISION (continued) 

D. R. WHITE, Chairman 

E. I. du Pont de Nemours and Company 

Parlin, N. J. 

R. B. AUSTRIAN A. N. GOLDSMITH 

F. T. BOWDITCH T. T. GOLDSMITH, JR. 

F. E. CAHILL HERBERT GRIFFIN 

A. W. COOK C. F. HORSTMAN 

E. D. COOK L. B. ISAAC 

C. E. DEAN P. J. LARSEN 

BERNARD ERDE C. LARSON 

R. L. GARMAN NATHAN LEVINSON 

FRANK GOLDBACH J. P. LIVADARY 

P. C. GOLDMARK H. B. LUBCKE 

THEATER TELEVISION 



PIERRE MERTZ 

H. C. MlLHOLLAND 

W. C. MILLER 

J. R. POPPELE 

PAUL RAIBOURN 
OTTO SANDVIK 
G. E. SAWYER 
R. E. SHELBY 
E. I. SPONABLE 
H. E. WHITE 



To make recommendations and prepare specifications for the construc- 
tion, installation, operation, maintenance, and servicing of equipment 
for projecting television pictures in the motion picture theater, as well as 
projection-room arrangements necessary for such equipment, and such 
picture-dimensional and screen-characteristic matters as may be in- 
volved in high-quality theater-television presentations. 

D. E. HYNDMAN, Chairman 

342 Madison Ave. 
New York 17, N. Y. 

P. J. LARSEN, Vice-Chairman 

508 S. Tulane St. 
Albuquerque, N. M. 



NATHAN LEVINSON 
OTTO SANDVIK 
EDWARD SCHMIDT 
E. I. SPONABLE 
J. E. VOLKMAN 



G. L. BEERS E. P. GENOCK 

F. CAHILL A. N. GOLDSMITH 

A. W. COOK T. T. GOLDSMITH, JR. 

JAMES FRANK, JR. C. F. HORSTMAN 

R, L. GARMAN L. B. ISAAC 

A. G. JENSEN 

TEST-FILM QUALITY 

To supervise, inspect, and approve all print quality control of sound and 
picture test films prepared by any committee on engineering before the 
prints are released by the Society for general practical use. 

F. S. BERMAN, Chairman 

111-14 76th Ave. 
Forest Hills, L. L, N. Y. 



F. R. WILSON 



C. F. HORSTMAN 



322 



COMMITTEES OF THE SOCIETY 



THEATER ENGINEERING, CONSTRUCTION, AND 
OPERATION 

To make recommendations and prepare specifications of engineering 
methods and equipment of motion picture theaters in relation to their 
contribution to the physical comfort and safety of patrons, so far as can 
be enhanced by correct theater design, construction, and operation of 
equipment. 

LEONARD SATZ, Chairman 

132 W. 43rd St. 
New York 18, N. Y. 



FELIX ALEXA 
HENRY ANDERSON 
A. G. ASHCROFT 
CHARLES BACHMAN 



F. E. CARLSON 
E. J. CONTENT 
JAMES FRANK, Jr. 



EVANS PERKINS 
BEN SCHLANGER 
SEYMOUR SEIDER 
EMIL WANDELMAIER 



SMPE REPRESENTATIVES TO OTHER ORGANIZATIONS 

AMERICAN STANDARDS ASSOCIATION 



Sectional Committee on: 
Standardization of Letter Symbols 
and Abbreviations for Science and 
Engineering, Z10 

S. L. CHERTOK 

Motion Pictures, Z22 

C. R. KEITH, Chairman 

A. N. GOLDSMITH, Honorary Chairman 

F. E. CARLSON E. K. CARVER 

D. F. LYMAN 



Sectional Committee on: 
Acoustical Measurements and Termi- 
nology, Z24 

F. C. SCHMID 
Photography, Z38 

J. I. CRABTREE 

Standards Council, ASA Member- 
Bodies 

D. E. HYNDMAN 



R. M. EVANS, Chairman 



INTER-SOCIETY COLOR COUNCIL RADIO TECHNICAL PLANNING 

BOARD 

P. J. LARSEN E. I. SPONABLE^ 

t Alternate. 

AMERICAN DOCUMENTATION 
INSTITUTE 
J. E. ABBOTT 



J. A. BALL L. E. CLARK 

F. T. BOWDITCH A. M. GijNDELFINGER 

M. R. BOYER H. C. HARSH 



64th Semiannual Convention 
SOCIETY OF MOTION PICTURE ENGINEERS 

Hotel Statler October 25-29 Washington 6, D. C. 



OFFICERS OF THE SOCIETY 

LOREN L. RYDER ............................... President 

DONALD E. HYNDMAN ........................... Past-President 

EARL I. SPONABLE ........... .' .................. Executive Vice-President 

JOHN A. MAURER ............................... Engineering Vice-President 

CLYDE R. KEITH ............................... Editorial Vice-President 

JAMES FRANK, JR ............................... Financial Vice-President 

WILLIAM C. KUNZMANN ......................... Convention Vice-President 

( 1 . TOEL LORANCE .............................. Secretary 

RALPH B. AUSTRIAN ............................ Treasurer 

New York, General Office 

BOYCE NEMEC .................................. Executive Secretary 

HELEN M. STOTE ............................... Journal Editor 

SIGMUND M. MUSKAT ........................... Office Manager 

DIRECTORY OF COMMITTEE CHAIRMEN 

LOCAL ARRANGEMENTS 

N. D. Golden, Chairman 

REGISTRATION AND INFORMATION 

W. C. Kunzmann, Chairman 
Assisted by E. R. Geib and J. C. Greenfield 

PAPERS PUBLICITY 

G. A. Chambers, Chairman Harold Desfor, Chairman 

J. E. Aiken, Vice-Chairman, Washington, D. C. Assisted by Leonard Bidwell 

LUNCHEON AND BANQUET LADIES' RECEPTION 

J. G. Bradley, Chairman Mrs. N. D. Golden, Chairman 

HOTEL AND INFORMATION MEMBERSHIP AND SUBSCRIPTION 

J. C. Greenfield, Chairman Lee Jones, Chairman 

PUBLIC-ADDRESS EQUIPMENT PROJECTION PROGRAM 16 MM 

W. P. Button, Chairman R. B. Dame, Chairman 

PROJECTION PROGRAM 35 MM 
H. F. Heidegger, Chairman 

A. Pratt, Vice-Chairman 
Assisted by officers and members of Washington Projectionists Local 224 

SEPTEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 323 



324 SEMIANNUAL CONVENTION September 

GENERAL INFORMATION 

Hotel Reservations and Rates 

The Hotel Statler, Washington, D. C., will be the Convention Headquarters. 
Room-reservation cards were mailed to the membership in August. These should 
be checked to indicate the accommodations desired for the 64th Semiannual Con- 
vention and returned to the hotel promptly, so that the hotel can book and confirm 
room reservations. 

Reservations are subject to change of arrival date or cancellation prior to Oc- 
tober 10. 

The following daily rates (European Plan) are extended SMPE members and 
guests. 

Single room, with tub and shower, $4.50 to $7.50 
Double room, with tub and shower, $8.00 to $10.00 
Twin beds, with tub and shower, $9.00 to $13.00 
Parlor suites, with connecting bedroom, $17.50 to $26.50 

Rail, Pullman, and Plane Travel 

The Convention Committee suggests arranging travel accommodations at 
least a month prior to the Convention, since travel conditions still remain acute, 
especially into Washington, D. C. 

Convention Registration and Papers Program 

The Papers Committee can only function successfully in the early assembly, 
scheduling, and release of the tentative and final Convention programs by re- 
ceiving the title of paper to be presented, name of the author, and a complet 
manuscript mailed to one of the following vice-chairmen of this committee : 



J. E. AIKEN N. L. SIMMONS 

225 Orange St., S. E. 6708 Santa Monica Blvd. 

Washington 20, D. C. Hollywood 38, Calif. 

E. S. SEELEY H. L. WALKER R. T. VAN NIMAN 

250 W. 57th St. P. O. Drawer 279 4431 W. Lake St. 

New York 19, N. Y. Montreal 3, Que., Canada Chicago 24, 111. 



The Convention business and technical sessions will be held in the Presidential 
Ballroom of the hotel. Registration and Information Headquarters will be set up 
in the Capitol Terrace, adjacent to the Presidential Ballroom. All persons at- 
tending the Convention should register and receive their Convention badges, also 
identification cards, which will admit them to all sessions held at, and away from, 
the hotel. These cards also will be honored at the de luxe motion picture theaters 
in Washington. Only through your registration can the Society derive the 
revenue needed to defray the Convention expenses. Please co-operate. Conven- 
tion Press Headquarters and headquarters of Harold Desfor, SMPK Publicity 
Committee Chairman, will be located in the Continental Room. 



1948 SEMIANNUAL CONVENTION 325 

Special Meeting 

It is expected that the Thursday evening meeting will be held at a naval station. 
Tickets will be required for admission to this meeting, which can be obtained at 
the time of registration. Noncitizens will be required to register on Monday if 
they wish to attend this meeting. Busses will be available for transportation and, 
due to naval security regulations, all those attending will be required to go on such 
busses for which there will be a small charge. 

Convention Get-Together Luncheon 

The 64th Semiannual Convention Get-Together Luncheon will be held in the 
hotel's Congressional Room at 12:30 P.M. on Monday, October 25. Although 
there will be no technical session scheduled for that morning, Registration Head- 
quarters will be open from 9:30 A.M. to noon in the hotel's Capitol Terrace, so 
that you may register and purchase Luncheon and Banquet tickets. 

Seating at the luncheon will be assured only if tickets have been purchased from 
W. C. Kunzmann, who will be at the hotel several days before the Convention, 
or at the Registration Headquarters prior to noon on October 25. Only through 
your co-operation can the committee and hotel provide satisfactory accommoda- 
tions for this function. Checks or money orders made payable to W. C. Kunz- 
mann, Convention Vice-President, may be mailed to W. C. Kunzmann, c/o Hotel 
Staffer, Washington, D. C., from October 18-25 for Luncheon and Banquet tick- 
ets. Advance reservations should be picked up at Registration Headquarters. 
Tickets for the Luncheon must be purchased in advance and there will be no re- 
fund for tickets not used. 

Luncheon and Banquet fees will be announced in the Convention bulletin, pub- 
| lished in the October Journal. 

Convention Social Cocktail Hour 

The Convention Cocktail Hour for holders of Banquet tickets will be held in 
the Hotel Statler on October 27 in the Congressional room. 

Informal Banquet 

The Convention informal banquet (dress optional) will be held in the Presiden- 
tial Ballroom on the evening of October 27. At this time the annual Awards will 
be presented, and there will be dancing and entertainment. 

Table reservations should be made at the Registration Headquarters. No 
tables for the Banquet will be reserved except for holders of tickets that have been 
purchased before noon of October 27, and there will be no refunds for tickets not 
Used. 

Ladies' Headquarters and Registration 

The Ladies' Reception and Registration Headquarters will be located in the 
Potomac Room in the hotel, and open daily during the Convention dates, from 
10:00 A.M. to 5:00 P.M. Mrs. Nathan D. Golden will serve the Convention as 
Hostess to the visiting and local ladies attending the 64th Semiannual Convention. 
The ladies' entertainment program will be announced in later released convention 
bulletins. 



326 SEMIANNUAL CONVENTION 

Motion Pictures and Recreation 

The identification cards issued to registered members and guests will be hon- 
ored at the following motion picture theaters in downtown Washington: Loew's 
Capitol, Loew's Palace, Metropolitan, RKO Keith, and Warner. 

Literature and information will be available at the Registration Headquarters 
on the many places of historic interest in Washington and vicinity. The Con- 
vention recreational features will be released later by the local arrangements com- 
mittee. 

TENTATIVE PROGRAM 

Monday, October 25, 1948 

9:30 A.M. Registration, Capitol Terrace Room. Advance Sale of Luncheon 

and Banquet Tickets 

12 : 30 P.M. Get-Together Luncheon, Congressional Room 
3 : 00 P.M. Technical Session, Presidential Ballroom 
8:00 P.M. Technical Session, Presidential Ballroom 

Tuesday, October 26, 1948 

9:30 A.M. Registration, Capitol Terrace Room. Advance Sale of Banquet 

Tickets 

10:00 A.M. Technical Session, Presidential Ballroom 
2 : 00 P.M. Technical Session, Presidential Ballroom 
3:00 P.M. Business Session of the Society, Presidential Ballroom 
3 : 30 P.M. Resumption of Technical Session, Presidential Ballroom 

Open Evening 

Wednesday, October 27, 1948 

9:30 A.M. Registration, Capitol Terrace Room 

10:00 A.M. Advance Sale of Banquet tickets 

10:00 A.M. Technical Session, Presidential Ballroom 

Open Afternoon 

6:45 P.M. Cocktail Hour, Congressional Room 
8:00 P.M. 64th Semiannual Banquet, Presidential Ballroom 

Thursday, October 28, 1948 

Open Morning 

2:00 P.M. Technical Session, Presidential Ballroom 
8:00 P.M. Technical Session, location to be announced later 

Friday, October 29, 1948 

10:00 A.M. Technical Session, Congressional Ballroom 
2:00 P.M. Technical Session, Congressional Ballroom 
5:00 P.M. Adjournment of the 64th Semiannual Convention 



Section Meeting 



Cleveland Meeting 

The June 18, 1948, meeting of the Midwest Section was held in Cleveland, Ohio, 
at the General Electric Lighting Institute at Nela Park. Seventy-five guests and 
members attended this all-day affair and about twenty-five ladies attended the 
dinner and a special evening program. 

The doors were open at 9 : 30 A.M. and coffee was served during the registration 
period. 

At 10:00 A.M. the group was divided into smaller sections to visit the Sundeck 
Gallery, Horizon House, store, office, and school. Expertly handled demon- 
strations illustrated the methods used in creating lighting combinations which 
were truly dramatic and functional as well. 

At 11:30 A.M., R. T. Van Niman, chairman, called the meeting to order in the 
Auditorium. F. T. Bowditch gave a resume of the Report of the Standards com- 
mittee as presented in Santa Monica. Frank Carlson was called upon as the 
representative of our host, the General Electric Lighting Institute, and welcomed 
all to Nela Park. 

Gordon Chambers reported on the Santa Monica convention. He began with a 
series of Kodachrome slides which were projected on a large screen showing the 
Del Mar Beach Club, the surrounding territory, and some prominent members of 
the Society of Motion Picture Engineers. Mr. Chambers then summarized a few 
of the papers presented at the 63rd Semiannual Convention. Also he reported 
the high spots in the group of color papers which were presented on the coast. 

"The Engineering Aspects of Drive-In Theaters," by George M. Peterson, 
Cleveland, Ohio, was next presented by the author. It was revealed in this paper 
that there are approximately 800 drive-in theaters in this country with average 
capacity for 500 cars each. Mr. Peterson stated that many operators "build 
their theaters- without any engineering assistance," a fact which he greatly de- 
plored. Subjects covered in this paper were: traffic problems, grading, ramps, 
sound circuits, surfacing, and screen building. 

At 1:00 o'clock one half of the group visited the Automotive Lighting Labora- 
tory, and the other half visited the Optical and Photographic Laboratories. After 
' luncheon, which was served in the Cafeteria, the groups were reversed for visits 
to the Optical and Photographic Laboratories and the Automotive Lighting 
Laboratory. 

The meeting was resumed in the Auditorium, with R. T. Van Niman presiding, 
at 3:15 P.M. 

"Practical Applications of New Photographic Techniques," by John Campbell, 
vice-president, Jam Handy Organization, was supplemented by an 800-foot reel 
of 16-mm pictures showing samples of the various techniques described in the 
paper. "Light Sources for Television Studio Lighting," was given by Richard 
Blount of the General Electric Company. M. D. Temple of the Brush Develop- 
ment Company presented his talk, "Some Applications of Magnetic Recording 
in the Motion Picture Field," from a reel of tape which was recorded a few days 
previously in his living room and edited to match the series of slides which were 
simultaneously projected. Boyce Nemec, executive secretary of the SMPE, gave 

327 



328 



SECTION MEETING 



September 




R.T.VanNiman, 
chief sound engi- 
neer for Motio- 
graph, chairman of 
the Midwest Sec- 
tion, and in charge 
of the program, and 
Frank E. Carlson, 
General Electric 
Lamp Department 
illuminating engi- 
neer and host to 
the group. 



Typical scenes at the General Electric Lighting Institute, Nela Park, where 
the Midwest Section of the Society of Motion Picture Engineers held its June 
meeting at Cleveland. Nearly seventy members were in attendance for the 
day portion of the program. 



Frank E. Carlson 
lights a tiny grain- 
of- wheat lamp with 
a huge 50-kilowatt 
lamp for R. T. Van 
Niman and G. W. 
Colburn, president 
of the G. W. Col- 
burn Laboratories 
and secretary-treas- 
urer of the Mid- 
west Section. 




1948 SECTION MEETING 329 

a rather complete report on "Flicker in Motion Pictures; Further Studies," by 
L. D. Grignon, Twentieth Century-Fox Film Corporation. This paper was pre- 
sented at Santa Monica in May and was considered an important contribution to 
tho art for design of future equipment. 

At 5:15 P.M. the meeting adjourned for refreshments at the Coffee Bar for 
members, guests, and their ladies. This was followed by dinner, which was served 
hi the Managers' dining room. The only speech was by Mr. Van Niman leading 
a rising vote of thanks to our hosts, the General Electric Lighting Institute. 

At 7:00 P.M. a popular lecture by Alston Rodgers of the General Electric 
Company called, "New Horizons in Lamp Research," was given. This was a 
combination magic and vaudeville show with amazing stage props which was 
highly entertaining and enlightening to engineer and layman alike. 

"A Gearless, Sprocketless 8-Mm Projector," by Otto R. Nemeth, included a 
demonstration of this new 8-mm projector following a discussion of engineering 
features. This projector without gears or sprockets is driven directly from motor 
to shutter and cam shaft with a belt. The lamp is 750 watts, lens //1. 6, one inch, 
coated, and the mechanism is built into a self-contained carrying case with total 
weight 12y 2 pounds. 

Mr. Nemeth then gave a brief description of "A Professional Wire Recorder 
for Studio Use." The complete paper was presented at the Santa Monica Con- 
vention. This machine features a magazine for handling the wire and automatic 
threading. 

"The Optimum Performance of High-Brightness Carbon Arcs," was next pre- 
sented by F. T. Bowditch and M. T. Jones of the National Carbon Company. 
The arc trim described is applicable to studio lighting. The 16-mm positive and 
11-mm negative carbon holders are water-cooled jaws. Current at the crater is 
about 450 amperes. The light output is in excess of 40,000 lumens. 

"Tungsten-Filament Sources for Picture Projection," by D. A. Pritchard, of 
the General Electric Company, dealt with photometric measurements of various 
places in the optical system of a group of competitive projectors. The measured 
results indicate output performance as a percentage of light output. The report 
clearly indicated that peak performance may be obtained from standard equip- 
ment if there is proper alignment of the tungsten filament. 

"A Photometric Analysis of Picture-Projection Systems," by Edward E. Bickel 
of the Simpson Optical Manufacturing Company, was comprised of a mathemati- 
cal and geometrical analysis of factors limiting the light output of motion picture 
projection systems. Based on mathematical values, performance results were 
computed that compared with actual laboratory test results. The formulas given 
establish limits beyond which it is physically impossible to go. 

While the foregoing papers were presented, the ladies attended special demon- 
strations at "Horizon House" by Aileen Page and "Color and Indoor Sunshine" 
by Alston Rodgers. 



Book Review 



The Preparation and Use of Visual Aids, by Kenneth B. Haas and 
Harry G. Packer 

Published (1946) by Prentice-Hall, Inc., 70 Fifth Avenue, New York 11,. 
N. Y. 218 pages + XII pages + 6-page index. 167 illustrations. 6 x /4 X 9 x /4 
inches. Price, $4.00. 

Unique in a long procession of recent publications in the field of the preparation 
and use of audio-visual materials, this book provides a truly how-to-do-it ap- 
proach. Tempered with enough of the philosophical to point out clearly the 
strengths and advantages, in terms of the learning process inherent to the use of 
the several mechanical divisions within the broad medium of audio-visual pres- 
entation, detailed explanation continues to show how in the local training 
situation the preparation of valuable teaching materials may be undertaken. 

Designed primarily for use in personnel training, sales demonstrations, adult- 
education programs, and advertising, the book should find a use or place in the 
school professional library as well. 

Stress is continually made that visual materials are to be regarded as necessary 
supplementing experiences to good training programs. Too often the impression 
is given that here is a "new broom." Rather, this book stresses the idea that 
visual materials are not intended to displace but rather to improve and to supplement. 

The authors, Packer and Haas, have very methodically organized the discussion 
of the several audio- visual materials: motion pictures, filmstrips, slides, opaque 
projection, flash cards, maps, charts, posters, manuals, photographs, the black- 
board, the bulletin board, the field trip, objects and specimens, and television. In 
each case they have ended the chapter considering the several materials with a 
detailed "how to arrange it," "how to do it," set of instructions regarding pro- 
jection equipment and the production of the materials to be projected. 

The book is well illustrated and includes numerous sketches and photographic 
examples to help the interested person to follow out the thinking and helpful ideas 
stressed in the book indeed a valuable addition to the growing literature in this 
field. 

W. A. WlTTICH 

Bureau of Visual Instruction 

University of Wisconsin 

Madison 6, Wis. 

FORTY YEARS AGO 

Moving Pictures for Medical Students 

In one of the New .York hospitals moving pictures have been made 
of epileptic patients, as well as of persons affected with locomotor ataxia. 
This is following the example set in Vienna, where moving pictures have 
been made of celebrated surgeons performing critical operations. THe 
purpose in both cases is, of course, to enable students and practitioners 
to study the peculiarities of diseases and the methods of distinguished 
operators. 

The Moving Picture World, April 18, 1908 

330 






Journal of the 

Society of Motion Picture Engineers 

VOLUME 51 OCTOBER 1948 NUMBER 4 



PAGE 

Improved Safety Motion Picture Film Support 

CHARLES R. FORDYCE 331 

Color-Television Film Scanner BERNARD ERDE 351 

35-Mm Process Projector 

HAROLD MILLER AND E. C. MANDERFELD 373 

New Theater Loudspeaker System 

H. F. HOPKINS AND C. R. KEITH 385 

Modern Film Re-Recording Equipment 

WESLEY C. MILLER AND G. R. CRANE 399 

Motion Picture Research Council W. F. KELLEY 418 

Use of 16-Mm Motion Pictures for Educational Reconditioning 

EDWIN W. SCHULTZ 424 

Report of Studio-Lighting Committee 431 

Proposed 16-Mm and 8-Mm Sprocket Standards .' 437 

Thomas Armat 441 

Louis Lumiere 442 

Thad C. Barrows 442 

Book Reviews: 

"Enlarging Technique of the Positive," by C. I. Jacobson 

Reviewed by Joseph S. Friedman 443 

" Camera and Lens," by Ansel Adams 

Reviewed by Lloyd E. Varden 443 

"Informational Film Year Book 1947" 

Reviewed by Glenn E. Matthews 444 

Current Literature 445 

Journal Exchanges 446 



ARTHUR C. DOWNES HELEN M. STOTE GORDON A. CHAMBERS 

Chairman Editor Chairman 

Board of Editors Papers Committee 



Subscription to nonmembers, $10.00 per annum; to members, $6.25 per annum, included in 
their annual membership dues; single copies, $1.25. Order from the Society's general office. 
A discount of ten per cent is allowed to accredited agencies on orders for subscriptions and 
single copies. Published monthly at Easton, Pa., by the Society of Motion Picture Engineers, 
Inc. Publication Office, 20th & Northampton Sts., Easton, Pa. General and Editorial Office, 
342 Madison Ave., New York 17, N. Y. Entered as second-class matter January 15, 1930, 
at the Post Office at Easton, Pa., under the Act of March 3, 1879. 

Copyright, 1948, by the Society of Motion Picture Engineers, Inc. Permission to republish 
material from the JOURNAL must be obtained in writing from the General Office of the Society. 
Copyright under International Copyright Convention and Pan-American Convention. The 
Society is not responsible for statements of authors or contributors. 



Society of 

Motion Picture Engineers 

342 MADISON AVENUE NEW YORK 17, N. Y. TEL. Mu 2-2185 
BOYCE NEMEC EXECUTIVE SECRETARY 



OFFICERS 

1947-1948 



PRESIDENT 

Loren L. Ryder 

5451 Marathon St. 

Hollywood 38, Calif. 
PAST-PRESIDENT 

Donald E. Hyndman 

342 Madison Ave. 

New York 17, N. Y. 
EXECUTIVE VICE-PRESIDENT 

Earl I. Sponable 

460 West 54 St. 

New York 19, N. Y. 



EDITORIAL VICE-PRESIDENT 

Clyde R. Keith 

233 Broadway 

New York 7, N. Y. 
CONVENTION VICE-PRESIDENT 

William C. Kunzmann 

Box 6087 

Cleveland, Ohio 
SECRETARY 

G. T. Lorance 

55 La France Ave. 

Bloomfield, N. J. 






1948-1949 



ENGINEERING VICE-PRESIDENT 
John A. Maurer 
37-0131 St. 
Long Island City 1, N. Y. 

TREASURER 

Ralph B. Austrian 
25 W. 54 St. 
New York, N. Y. 

Governors 



FINANCIAL VICE-PRESIDENT 
James Frank, Jr. 
426 Luckie St., N. W. 
Atlanta, Ga. 



John W. Boyle 

1207 N. Mansfield Ave. 
Hollywood 38, Calif. 
David B. Joy 
30 E. 42 St. 
New York 17, N. Y. 



1947-1948 

Robert M. Corbin Charles R. Daily 

343 State St. 5451 Marathon St. 

Rochester 4, N. Y. Hollywood 38, Calif. 

Hollis W. Moyse 

6656 Santa Monica Blvd. 



Hollywood, Calif. 



William H. Rivers 
342 Madison Ave. 
New York 17, N. Y. 



1948 

S. P. Solow 
959 Seward St. 
Hollywood, Calif. 

1948-1949 



Alan W. Cook 
4 Druid PI. 

Binghampton, N. Y. 



Lloyd T. Goldsmith 

Burbank, Calif. 
Paul J. Larsen 
Los Alamos Laboratory 
University of California 
Albuquerque, N. M. 
Section Officers and Office Staff listed on page 447. 



R. T. Van Niman 
4431 W. Lake St. 
Chicago, 111. 



Gordon E. Sawyer 
857 N. Martel St. 
Hollywood, Calif. 



Improved Safety 

Motion Picture .Film Support 5 

BY CHARLES R. FORDYCE 

EASTMAN KODAK COMPANY, ROCHESTER, NEW YORK 



Summary Extensive experimental work on safety cine film support has 
resulted in an improved product which offers possibilities for professional 
motion picture use. 

This product is a highly acetylated cellulose acetate with physical proper- 
ties which are considerably different from those of ordinary commercial 
cellulose acetate previously used. Certain improved physical characteristics 
and improved aging properties of this base material are described in detail. 

As a cine positive film support the high-acetyl cellulose acetate is shown to 
give satisfactory behavior in printing, processing, and projection operations 
and compares favorably with present standard release positive film. 

Experimental studies on the use of the high-acetyl base for 35-mm nega- 
tive film are described showing that this base will lend itself to use for nega- 
tive materials. Particularly important is the fact that this base offers a very 
low degree of shrinkage on long time keeping. 

THE MOTION PICTURE industry has for many years employed two 
types of film stock; one on cellulose nitrate base for professional 
use, and the other on cellulose acetate base mostly in widths of less 
than 35 mm. The requirement of safety for amateur film has made 
the use of acetate necessary in this field, regardless of its comparative 
qualities in other respects. An improved safety-base stock, made of 
a cellulose acetate propionate was adopted by the Eastman Kodak 
Company in 1937, and afforded physical properties midway between 
those of cellulose nitrate and the former acetate. The character- 
istics of these films were discussed in detail by Calhoun 1 in 1944. 

The cellulose acetate propionate base was an improvement over 
cellulose acetate in many respects. It was less subject to brittleness 
at low humidities, and more resistant to dimensional change by 
moisture under varying conditions. During the war years of 1941 to 
1945 this safety film gave very satisfactory service for many purposes, 
including theater use for short subjects. . For rigorous professional 
motion picture use, however, this product fell somewhat short of 
requirements. Its comparatively low strength provided insufficient 

* Presented May 17, 1948, at the SMPE. Convention in Santa Monica. 

OCTOBER, 1948 JOURNAL OF THE SMPE VOLUME 51 331 



332 FORDYCE October 

wearing qualities and it lacked necessary rigidity for screen steadiness 
in projection with high-intensity lamps. For these reasons still 
further improvements, particularly in strength and rigidity of the 
base, were desirable. 

In continued experimental work toward further improvements in 
safety base it has been found that of all plastic materials which have 
offered potential possibilities of better quality film support, the 
product most promising was a cellulose acetate selected in the range 
of higher degrees of acetylation than the product commonly used. 

In the manufacture of cellulose acetate a hydrolysis step is usually 
employed to remove part of the acetyl groups and provide a material 
soluble in acetone. To gain this advantage in- solubility the product 
is transformed from a strong, more rigid, very neat-resistant acetate 
to one more plastic. This is adverse to the basic requirements of 
good film support. 

Cellulose triacetate, the product of complete acetylation of cellulose 
is soluble in only a limited number of organic solvents, and would be 
of doubtful success for motion picture film base because of the diffi- 
culty of splicing. Furthermore, casting procedures are difficult with 
this material, tending to give brittle film. By selecting an inter- 
mediate chemical composition, within the range of 42.5 to 44.0 per cent 
acetyl content, it has been found possible to retain the advantages of 
high physical strength and at the same time eliminate the problem of 
proper manufacturing quality and splicing behavior. 

The chemical nature of these safety base materials is shown graph- 
ically in Fig. 1. The trilinear chart is used to show the relative 
chemical compositions of cellulose acetates and cellulose acetate pro- 
pionates. 2 Cellulose acetates of different acetyl contents lie along the 
left boundary line of the triangle. Cellulose propionates are iden- 
tified along the right boundary line. Within the area of the triangle 
are mixed esters of acetic and propionic acid. Cellulose triacetate 
(44.8 per cent acetyl) and cellulose tripropionate (51.8 per cent pro- 
pionyl) are identified at points which mark complete esterification of 
the cellulose. Point A identifies the commercial acetone-soluble cel- 
lulose acetate used in safety base before 1937. The range B designates 
the material used in the present new safety-base development. With- 
in the area of the triangle the point C identifies the cellulose acetate 
propionate used as Eastman Safety Base since 1937. 

The new safety base has proved to be a useful improvement for 
both 35-mm and narrow-width motion picture films and is being used 



1948 



SAFETY FILM SUPPORT 



333 



at the present time for some Eastman films. These include safety 
release positive film, in both 16-mm and 35-mm widths, as well as the 
32-mm width film, later to be converted to 16-mm product; fine-grain 
duplicating positive film, type 5365, in both 35-mm and 16-mm 
widths; sound-recording film, type 5373, in both 35-mm and 16- 
mm widths; and high-contrast positive film, type 5363, in 16-mm 
width. In addition, the new base is being used for certain profes- 
sional 35-mm duplitized-color positive films. 

CELLULOSE 



CELLULOSE 
TRIACETATE 



ACETYL 




CELLULOSE 

- TRIPROPIONATE 



PROPIONYL 



Fig. 1 Chemical composition of cellulose esters used in safety film base. 
A, acetone-soluble cellulose acetate; B, high-acetyl cellulose acetate; 
C, cellulose acetate propionate. 

Careful evaluation of this base for 35-mm film indicates it should 
be suitable for professional motion picture positive and negative 
stock, for which cellulose nitrate base is now employed. The results 
of these tests are summarized in the following experimental sections. 

PROPERTIES OF FILM BASE 

Consideration of the physical properties of the film base will serve 
as a comparison of the high-acetyl cellulose acetate support with 
nitrate and safety products which have been in standard use (Table 
I) . In these measurements both lengthwise and width wise directions 
of the support have been included because of the slight difference in 
these two directions. In certain cases such differences may be of 
importance. 



334 



FORDYCE 



October 



B 



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02 



1948 



SAFETY FILM SUPPORT 



335 



The tensile strength of the high-acetyl base is considerably im- 
proved over the former safety base and approaches that of the nitrate, 
indicating a corresponding increase in the mechanical wearing 
quality of the material. Flexibility is of importance in general 
handling behavior, and is in the same range for all three products. 
Tear values of the high-acetyl base are somewhat below those of 
cellulose nitrate and acetate propionate, and may be the cause of 
some concern if this property should prove to be critical. Young's 
modulus is a measure of the stiffness and rigidity of the support and is 



100 



80 



2 60 



40 



20 




B \. 



Q) 



s*< 

f ^HIGH ACETYL SAFETY 

^ ACETATE PROPIONATE SAFETY 



10 



20 



25 



30 



TIME. DAYS 



Fig. 2 Viscosity retention of film base at 100 degrees centi- 
grade. 

of importance in resisting temporary or permanent deformation. The 
high-acetyl base here shows appreciable improvement over the former 
safety base, and is somewhat inferior to the nitrate. Cold flow 
characteristics represent the tendency of the material to undergo 
permanent deformation under stress. Here again, the high-acetyl 
base lies midway between the other two products. 

A further evaluation of the film base may be made by testing its 
permanence under accelerated aging. These tests involve heating 
samples for periods of time at temperatures above those which 
ordinarily would be met in standard use with the assumption that 
this severe condition will predict their behavior for much longer 
periods of time in normal use. No quantitative relation between 



336 



FORDYCE 



October 



accelerated and normal keeping times can be given. It may be 
pointed out, however, that a National Bureau of Standards test for 
Archive films 8 employs an incubation time of three days at a temper- 
ature of 100 degrees centigrade. 

The chemical stability of cellulose derivatives is best measured by 
their resistance to viscosity degradation. Samples of film support 
may be incubated at elevated temperatures for periods of time after 
which they may be dissolved in suitable solvents and the viscosities 
compared with those of the same material before heating. Chemical 
deterioration results in loss of viscosity which is proportional to the 
degree of degradation. Viscosity curves of safety and nitrate film 




5 10 15 20 

TIME. DAYS 

Fig. 3 Retention of flexibility of film base at 100 degrees 
centigrade. 

support upon heating at 100 degrees centigrade for increasing periods 
of time are given in Fig. 2. It will be noted that the safety bases 
undergo this treatment with no appreciable chemical degradation, 
while cellulose nitrate rapidly and progressively decreases in vis- 
cosity. This comparative behavior is well known, and illustrates the 
possibilities of distinctly superior keeping qualities of cellulose ace- 
tate safety base. 

Flexibility retention in accelerated aging tests at 100 degrees centi- 
grade is shown in Fig. 3. Very little loss in flexibility up to 30 days 
at this temperature has resulted in either safety base, from which it 
may be pre:licte 1 that very long times, under standard storage 
conditions, should be possible without difficulty. Cellulose nitrate 



1948 



SAFETY FILM SUPPORT 



337 



support dropped rapidly in flexibility at this temperature, and became 
completely brittle within ten days. 

As an indication of the retention of tear strength the curves of Fig. 
4 give measurements of tear values of the three film bases after in- 
creasing periods of incubation. Although the high-acetyl safety 
base has somewhat lower initial tear values than the other products, 
the fact that there is little or no loss in tear strength under this very 
severe incubation indicates probable satisfactory behavior in film use. 
Cellulose nitrate support again deteriorates rapidly under this 
treatment. 



80 















I 




ACETATE PROPION/ 


TE SAFET1 




\ 


D 










T~r 

\ NITRATE 

\ 
\ 


HIGH 


ACETYL 


SAFETY 




(SHATTERS) 













10 



15 
TIME. DAYS 



20 



25 



30 



Fig. 4 Retention of tear strength of film base at 100 de- 
grees centigrade. 

An important property of motion picture film is its permanence of 
dimension upon aging. Results of accelerated shrinkage tests on the 
base at 100 degrees centigrade are shown in the curves of Fig. 5. It 
will be noted that the high-acetyl base here exhibits a lower order of 
shrinkage than either the safety or nitrate standard materials. Be- 
cause of the severe temperature used in this test, a second series of 
shrinkage measurements were carried out at 71 degrees centigrade 
(160 degrees Fahrenheit) to confirm this shrinkage behavior (Fig. 6). 
Here again, the high-acetyl base exhibited a very low order of shrink- 
age as compared with the other materials. From these character- 
istics it may be predicted that the experimental base should give film 
of excellent aging shrinkage properties. 

To summarize the physical properties of the base materials, the 
high-acetyl cellulose acetate is an improvement over former safety 



338 



FORDYCE 



October 




TIME. DAYS 

Fig. 5 Rate of shrinkage (lengthwise) of motion picture posi- 
tive film base at 100 degrees centigrade. 

base in most of its properties, and particularly in tensile strength and 
rigidity, which are most needed. Compared with cellulose nitrate, 
most properties are somewhat lower in original measurements, but 
permanence tests show that there is very little change in quality even 
under severe aging tests. Perhaps the most unique property of the 



U3 

1.00 
0.75 
0.50 
0.25 
n 






A 


CETATE PRC 


>PIONATE S* 


FETY 


D < 


^v 


,^--* D " 










^A' 




NITRATE 




. A - 








o ' 




HIGH ACETYL SAFETY 


. -o 








L 













10 15 20 

TIME. DAYS 



25 



30 



Fig. 6 Rate of shrinkage (lengthwise) of motion picture 
positive film base at 71 degrees centigrade (160 degrees 
Fahrenheit). 



1948 SAFETY FILM SUPPORT 339 

high-acetyl acetate is its exceptionally low shrinkage as compared with 
materials previously in use. 

PROPERTIES OF CINE FILM 

Proper evaluation of the experimental film base for cine products 
requires consideration of its use as both positive and negative stock. 
In the case of positive films, processing, printing, and projection be- 
havior should be considered in detail. Negative products introduce 
the factors of camera behavior and proper shrinkage characteristics 
as additional important qualities. 

Positive 85-Mm Film 

Testing of positive 35-mm films was done by comparison with stand- 
ard safety release print stock (5302) on cellulose acetate propionate 
base and nitrate release print stock (1302). 

Processing Tests An important factor in processing motion 
picture film is the degree of swelling which takes place in the develop- 
ing step. If the longitudinal swell is too rapid or too great some 
processing machines encounter trouble from excessive slackness which 
allows the film to become displaced on the bottom rollers. Likewise, 
excessive swelling during development may result in correspondingly 
excessive shrinkage at the beginning of the drying operation. This 
has been a difficulty with previous safety films, not only because of the 
magnitude of swelling, but also because of the very rapid rate of 
shrinkage of the safety film upon drying, causing rapid building up of 
tension in a critical area. Of importance also is any tendency which 
the film may have to curl too highly negative (away from the emul- 
sion) at the beginning of drying, or too highly positive (toward the 
emulsion) when completely dry. 

Results of preliminary processing tests are summarized in Table II. 
The curl characteristics of the high-acetyl film will be seen to be of the 
same order as the standard check materials. A slight positive curl 
takes place after fixing which changes to a slight negative curl at the 
beginning of the drying operation. This changes again to a positive 
curl when leaving the drying cabinet, which returns to a very slight 
positive curl at the time of rewinding. The development shrinkage 
is also of small magnitude, and characteristic of present product. 
The lengthwise swelling of the experimental film during processing is 
0.28 per cent. This is slightly greater than the type 1302 nitrate film, 
but less than the acetate propionate safety 5302 material. 

The swelling and shrinkage behavior of these films may be seen in 



340 



FORDYCE 



October 



more detail in Fig. 7. Upon immersion in water the lengthwise 
swelling takes place quite rapidly for about 30 minutes then ap- 
proaches a maximum value. The rates of shrinkage upon drying 
after 30 minutes' swelling are shown by descending curves. It will 
be seen that during the first ten minutes of drying the high-acetyl 
film shrinks 0.14 per cent, the nitrate 0.07 per cent and the acetate 
propionate safety 0.31 per cent. Thus, while the high-acetyl film 
exhibits an appreciable amount of swelling its comparatively slow 




TIME. MINUTES 

Fig. 7 Rates of swell in water at 68 degrees Fahrenheit (heavy 
curves) and rates of shrinkage upon drying at 70 degrees Fahrenheit, 
50 per cent relative humidity (light curves) for positive films. 

rate of shrinkage upon drying tends to reduce the possibility of 
excessive operating tensions. 

Following these preliminary measurements extensive processing 
tests were carried out in two commercial East Coast Laboratories 
each test involving several thousand feet of film, to insure in so far as 
possible that the test represented stable continuous processing 
behavior. In these tests the experimental product proved to be 
satisfactory, giving no "indication on any of the machines of greater 
tension than normal (Table III). Likewise, in none of the tests did 
the swelling during development cause difficulty from slackness. 

Projection Tests Evaluation of the projection quality of 35-mm 
positive film is probably the most important factor in the testing 
program. Many characteristics must be considered, and can only be 



1948 SAFETY FILM SUPPORT 341 

TABLE III 

PROCESSING OF HIGH-ACETYL 5302 (35-Mai) FILM 
Tests in Commercial Laboratories 





Machine 






Film 






Threading 


Approximate Curl at 




Length, 


Drying 


Feet of 


Rewind, 




Laboratory 


Feet 


Conditions 


Test 


Inch 


Difficulties 


A 


1750 


77 F. 42% R.H. 


21,000 


+0.09 


None 


B 


2120 


63 F. 60% R.H. 


12,000 


+0.14 


None 



determined by experimental projection under conditions of actual use. 
Preliminary tests of a laboratory nature were made in this investiga- 
tion, and were followed by trade tests involving prints of several 
commercial feature pictures issued through selected film exchanges in 
different parts of this country. 

Preliminary laboratory tests for physical behavior of the film in- 
volved continuous projection of short lengths of film for increasing 
lengths of time, followed by examination of the film for perforation 
damage and general appearance. A summary of the results is given 
in Table IV. It will be noted that slight perforation damage began 
to take place after about 200 projections for both the high-acetyl and 
the nitrate films, as compared with 100 projections for the acetate- 
propionate safety film. This became progressively more severe on all 
products until failure by complete perforation breakdown at 520 runs 
for the high-acetyl film as compared with 380 runs for the acetate- 
propionate safety and 644 for the nitrate. It should be emphasized 
that the numerical values of runs before failure are of significance only 
for comparative purposes, and do not necessarily indicate the number 
of runs to be expected in trade use. 

Another type of laboratory test involved projection of rolls of the 
three types of film on a Simplex E-7 projector, with a projection 
throw of 157 feet to a screen 30 feet by 40 feet. Initial tests with non- 
rotating positive high-intensity arcs up to 65 amperes in mirror 
optical system lamps resulted in entirely satisfactory performance of 
all three types of film. A more severe test was then undertaken, 
using a rotating positive high-intensity arc (13.6-mm positive carbon) 
at 175 amperes in a condenser optical system lamp and employing 
an Aklo No. 3966 heat-absorbing glass filter. Certain charac- 
teristic differences in the films became evident in this test, as recorded 
in Table V. The acetate propionate safety 5302 film here showed 



342 



FORDYCE 



October 



TABLE IV 
WEARING QUALITY OF MOTION PICTURE POSITIVE FILM 



Times 
Projected 


High-Acetyl 
Acetate 5302 


Acetate Propionate 
5302 


Nitrate 1302 


100 


A 


B 


A 


200 


B 


C 


B 


300 


C 


D 


B 


400 


D 


Failure (380) 


C 


500 


D 




D 


600 
700 


Failure (520) 





D 

Failure (644) 



Condition of Film 

A No perforation damage 
B Damage in one perforation in a frame 
C Damage in two perforations in a frame 
D Damage in three perforations in a frame 

considerable unsteadiness in focus, 4 and rather severe embossing 
after projection. The high-acetyl safety film and the nitrate 1302 
were satisfactory and nearly identical in behavior. Upon examina- 
tion after projection the high-acetyl film showed somewhat less 
embossing effect than the nitrate. 

On the basis of the above background, indicating satisfactory 
behavior of the high-acetyl film for commercial use in regard to both 



TABLE V 

LABORATORY PROJECTION QUALITY OF CINE POSITIVE FILM 
Arc Intensity: 175 Amperes 



High- 
Acetyl 
5302 



Acetate 

Propionate 

5302 



Nitrate 
1302 



Screen Quality 

Original sharpness and definition O.K. O.K. O.K. 

Focus drift Normal Excessive Normal 

Tendency to image flutter Slight Slight Slight 

Tendency to in-and-out of focus Slight Excessive Slight 

Film Appearance 

Frame embossing Very slight Appreciable Slight 

Image embossing Very slight Appreciable Very slight 



1948 SAFETY FILM SUPPORT 343 

processing and projection behavior, it was decided to undertake 
trade tests with prints released in the regular manner for theater use. 
In these tests, which included four different features and a total of 22 
experimental prints, each print was assembled with approximately 
half of the reels on the experimental stock and half on standard 
nitrate. The first two reels in each case were of one type of stock and 
the next two of the other, and so forth, to insure that each material 
would be used on both projectors in any theater. 

Throughout these tests no difference was noted between any of the 
experimental and standard reels as regards condition of focus, 
steadiness on the screen, or general quality of either picture or sound. 
Likewise no detectable difference was noted in the tendency toward 
scratching. The conditions of the prints after completion of their 
trade use are summarized in Table VI. All films were comparable 
throughout in curl and in brittleness at low humidity. Shrinkage of 
the experimental film was consistently less than that of the nitrate 
stock. Likewise the tendency of the film to become embossed or buckled 
after long use was noted to be less in the experimental film. In per- 
foration damage, no marked differences were evident, although the 
experimental films showed somewhat greater damage in areas of 
severe wear. This is in agreement with the preliminary projection 
tests, which indicated a slight advantage in mechanical wearing 
quality for the nitrate film, but is believed to be due in part also to 
the higher shrinkage characteristics of the nitrate, which give that 
material the advantage of more nearly fitting the projector sprockets. 

The lower shrinkage values noted for the experimental film in these 
practical use tests are in agreement with the predicted behavior ob- 
served in the accelerated shrinkage tests (Figs. 5 and 6) and have been 
further confirmed by laboratory keeping tests of processed film under 
normal conditions (Fig. 8). Here the high-acetyl film will be noted 
to undergo a shrinkage of 0.20 per cent in one year as compared with 
0.29 per cent for standard nitrate and a higher value of 0.46 per cent 
for film on cellulose-acetate propionate safety base. 

It may be well to point out in connection with these trade tests that 
they were carried out while all theaters were using 0.935-inch-diam- 
eter intermittent sprockets. Because of the recently adopted 
change in standard to the 0.943-inch-diameter sprocket it may be 
expected that the new sprockets will soon replace the former in most 
theaters. This will be an advantage to films with low shrinkage 
characteristics, such as this experimental material, and should offer 



344 



FORDYCE 



Oc1 



an improvement in wearing quality for high-acetyl cellulose acetat 
film even greater than that anticipated for film on nitrate base. 

Splicing The question of proper splicing behavior is one of im- 
portance for motion picture films. It was pointed out that the chem- 
ical composition of the cellulose acetate used in this film base is in a 
range of very limited solubility in organic solvents. This fact limits 
the formulation of effective cement mixtures to carefully chosen 
solvents, properly balanced to give good results with this specific 
product. For this reason it should not be expected that film cements 
designed for products previously in use should give good performance. 



0.6 



0.4 




TIME, MONTHS 

Fig. 8 Rate of shrinkage (lengthwise) of motion picture posi- 
tive films. Individual developed strips were stored, freely ex- 
posed to circulating air, and shrinkage values calculated from 
the initial dimension of the raw stock. 

It has been demonstrated, however, that properly formulated 
cements can be made without great difficulty, and suitable cements 
are now available for the purpose. With these the cementing prop- 
erties of the new film are quite similar to those of other types of film 
with cements commonly "used for them. 

Proper splicing behavior must in all cases be qualified with the re- 
quirement that the emulsion be scraped properly from the film support 
in the area to be cemented. It is essential here to remove the bonding 
sublayer beneath the emulsion so that the cement solvents will have 
sufficient opportunity to attack the film base. This removal of sub- 
layer is somewhat more critical on safety than on nitrate base, and 



SAFETY FILM SUPPORT 



345 



c 

1:1 

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II 

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pq ^ 





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d d 



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346 FORDYCE October 

should be understood properly by the operator. Duplitized cine films 
which carry emulsions on both front and back surfaces of the film, 
should be recognized as far more difficult to splice than single- 
coated films, and should receive special consideration in removal of 
sublayer coatings before cement is applied. 

Negative 35-Mm Film 

In general, mechanical properties which are necessary for positive 
film are also advantageous for negative. Its use on continuous 
printers, however, demands proper shrinkage characteristics to 
provide the necessary range of perforation pitch to give good printing 
quality. It is well understood that standard processing laboratory 
practice requires that negative films which are manufactured with 
the standard perforation pitch as raw stock undergo a shrinkage of at 
least 0.20 per cent for use as a negative on continuous drum printers. 5 ' 6 
A satisfactory range for good printing quality is usually considered to 
be a shrinkage of between 0.2 and 0.4 per cent. If shrinkage should 
exceed this range, however, the pitch becomes too short and again 
results in unsatisfactory prints. 

These shrinkage characteristics of negative film have been controlled 
during manufacturing by allowing a small but controlled amount 
of solvent to remain in the support. As this escapes from the film 
during processing and subsequent storage of one to three months a 
corresponding shrinkage takes place. 

A better way of meeting the requirements of negative film might be 
to employ a base of very low shrinkage properties and to change the 
standard of perforation so that the pitch will be optimum for printing 
throughout the life of the negative. For this to be successful tjie 
shrinkage upon aging would have to be exceptionally low, to main- 
tain good printing quality on long keeping. 

The low shrinkage characteristics of the experimental high-acetyl 
acetate base presented possibilities for such a product. To test this 
a set of experimental films was specially prepared, including both 
normal shrinkage and .low shrinkage base, perforated to both stand- 
ard and optimum pitch dimensions. These products are tabulated 
in Table VII. Sample A was made to correspond to standard nitrate 
negative (1231) in its shrinkage characteristics while samples B and C 
were made to represent low shrinkage films. This is shown by the 
"accelerated aging" measurements, which represent the degree of 
shrinkage which would normally take place over a considerable 






SAFETY FILM SUPPORT 



347 



9. 






00 00 00 O 

^1 i-H ^H CO 

dodo 



CO CO CO (N 

dodo 



12 o o 2 
dodo 



o o 



oo 






ll 



t bC M ^bfl -ij 



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8 



period of time. Sample B was per- 
forated with a pitch of 0.1869 inch 
and sample C with a shorter pitch 
of 0.1866 inch to correspond to a 
shrinkage of 0.20 per cent. 

Test rolls of each sample of nega- 
tive film were exposed in a Mitchell 
camera and were processed by 
standard procedure. These were 
used to make prints on standard 
fine-grain release positive (1302) 
stock shortly after processing and 
at repeated intervals of time over a 
period of several months. Results 
of printing quality were found to 
be in agreement with pitch values 
at the time of printing. The re- 
sults of shrinkage behavior are 
shown in Fig. 9. It will be seen 
that sample A reproduces in general 
the shrinkage behavior of the stand- 
ard (1231) negative, sample D. 
Both of these negatives gave some- 
what unsteady prints when printed 
soon after processing, but were 
satisfactory on later tests, by 
which time shrinkage had resulted 
in shorter pitch measurements. 
Sample C, on the other hand, cor- 
responded to a shrinkage of 0.20 
per cent when freshly processed 
because of perforation adjustment, 
and as a result gave immediate 
satisfactory printing quality. Also, 
because of its low shrinkage, it 
continued to give good printing 
quality after long keeping. As 
would be expected, the sample B 
with standard pitch perforations 
on low shrinkage base gave 



348 



FORDYCE 



October 



unsteady prints the first three months of the test period. 
These results indicate the possibility of obtaining a satisfactory 
safety cine negative film either by standard perforation of stock 
duplicating present negative film in shrinkage characteristics, or by a 
properly adjusted perforation of stock employing low shrinkage base. 
The latter product may prove to be attractive to the industry be- 
cause of its improved permanence characteristics and because of 
possible improved printing quality immediately after processing as 
well as after long aging. 




-0.6 



TIME, MONTHS 

Fig. 9 Change in longitudinal pitch of developed motion picture negative 
films stored in rolls in untaped cans. Film rewound daily for first 30 days. 

A, high-acetyl safety base, normal negative shrinkage, initial pitch 0.1869 
inch; B, high-acetyl safety base, low shrinkage, initial pitch 0.1869 inch; 
C, high-acetyl safety base, low shrinkage, initial pitch 0.1866 inch; D, ni- 
trate base, normal negative shrinkage, initial pitch 0.1869 inch. 

CONCLUSIONS 

1. An evaluation of an improved safety motion picture film sup- 
port, made from a high-acetyl type of cellulose acetate, has been 
presented. 

2. The general physical characteristics of the high-acetyl acetate 
base are superior to those of former safety base materials, and are in 
the range of base from cellulose nitrate. 

3. The properties of the new base have been confirmed by com- 
mercial tests of positive film in which satisfactory quality for pro- 
fessional motion picture use was obtained. 



1948 SAFETY FILM SUPPORT 349 

4. Laboratory tests on negative film have been carried out, which 
indicate probable satisfactory behavior. Low shrinkage character- 
; istics of the high-acetyl acetate base offer the possibility of improved 
i printing characteristics under proper conditions. 

ACKNOWLEDGMENT 

The author wishes to express his appreciation for the assistance and 

I helpful suggestions received from many members of the Department 

of Manufacturing Experiments of the Eastman Kodak Company in 

the preparation of this paper. 

- 

REFERENCES 

(1) J. M. Calhoun, "The physical properties and dimensional behavior of 
motion picture film," J. Soc. Mot. Pict. Eng., vol. 43, pp. 227-267; October, 1944. 

(2) C. J. Malm, C. R. Fordyce, and H. A. Tanner, "Properties of cellulose 
esters of acetic, propionic, and butyric acids," Ind. Eng. Ghent., vol. 34, p. 430; 
April, 1942. 

(3) J. R. Hill and C. G. Weber, "Stability of motion picture films as deter- 
mined by accelerated aging," Research Paper RP 950, Jour. Res. Nat. Bur. 
Stand., vol. 17, p. 871; December, 1936. 

(4) E. K. Carver, R. H. Talbot, and H. A. Loomis, "Effect of high-intensity 
arcs upon 35-mm film projection," J. Soc. Mot. Pict. Eng., vol. 41, pp. 69-88; 
July, 1943. 

(5) R. H. Talbot, "Some relationships between the physical properties and the 
behavior of motion picture film," J. Soc. Mot. Pict. Eng., vol. 45, pp. 209-218; 
September, 1945. 

(6) J. Crabtree, "Sound film printing," /. Soc. Mot. Pict. Eng., vol. 21, pp. 294- 
323; October, 1933. 

DISCUSSION 

CHAIRMAN W. V. WOLFE: Dr. Fordyce, I understand that your company is 
now putting out a universal film cement which is good for the old acetate and the 
new safety-base film. Is that correct, and do I also understand that you are no 
longer making available the old nitrate-base film cement? 

DR. CHARLES R. FORDYCE: The first part of that statement is correct. We 
are putting out a film cement which we call Universal Cement for all types of film. 
I think I am right in stating that you are also correct in the second statement that 
we no longer supply the other, but I might be wrong. 

CHAIRMAN WOLFE: I particularly ask that question because there has been 
some comment about the possibility that the Universal Cement was not so good 
for a nitrate-base film as the old nitrate film cement. 

DR. FORDYCE: Yes, that is a question. Of course, as you know, in testing 
film cements, it is quite difficult to get more than two people to test them in the 
same way, and I do not really know what a majority opinion would be on the 
basis of these two cements. We like the newer cement in the tests we have run, 
and in our use, but maybe some of the trade would rather have the other cement. 



350 FORDYCE 

DR. C. R. DAILY: Some years ago, we ran a series of pitch checks on release 
negative, starting with the first and printing from that negative, and then measur- 
ing successively 25, 50, and up to 300 prints during the release life of that negative. 
During that time the negative was aerated through the printer and rewound that 
many times, and pitch checks were made throughout the entire run to determine 
properties posted in the last slide that you showed, and to help determine the 
matter of initial pitch. Have you made live tests through a release print cycle for 
the aeration and pull on the negative to determine how the acetate film compares 
with nitrate? 

DR. FORDYCE: We have given you all the shrinkage data that we have; in 
other words, keeping tests, but not tests made at intervals during actual use of 
that negative. Our data are only laboratory incubation tests. I think quali- 
tatively that actual use data would have the same trend as our laboratory tests. 

MR. K. B. LAMBERT: We have used some of this film recently, both with the 
long perforation and some specially perforated. We have had very successful 
results from the shorter perforations. With the longer perforations, we con- 
stantly encountered unsteadiness on all of the early prints. In fact, we never got 
away from it until we short-perforated the film. 

The Research Council is at this time considering the possibility of recommend- 
ing, in conjunction with Eastman, the shorter perforation of this type of film, be- 
cause we are faced here with the problem of making the highest quality prints 
first, immediately after the negative is processed; then perhaps the negative lies 
idle for quite a while and some more prints are made, but if you can have a nega- 
tive which can be printed over a very long period of time, and have both the first 
and last prints all good, it would seem to be very advantageous. 

MR. G. J. BADGELY: As Eastman people are pretty well aware, we are inter- 
ested in high-temperature development. What is the action of this film when it 
is subject to developing temperature of 125 degrees? 

DR. FORDYCE: It is going to be a problem connected with the emulsion. We 
can say that this base is more resistant than former safety base but the degree of 
swelling in water is more than nitrate; if you increase the temperature, you have 
a higher amount of swelling. So far as I know, it is not high enough to interfere. 

QUESTION: Would there be any elasticity added to the film as a result of the 
higher temperature? Has it a tendency to stretch under strain? 

DR. FORDYCE: Yes, the higher the temperature, the softer it will be. In other 
words, it will be more easily distorted at the higher temperature but not so much 
so as prior safety films. 

DR. J. G. FRAYNE: It seems a shame that we are still worrying about printing 
from antediluvian sprocket- type printers. Instead of spoiling a fine job, why does 
not the whole industry do something about the printer situation? 

CHAIRMAN WOLFE : Dr. Fordyce cannot very well answer that question, nor 
for that matter, can anyone else answer for the industry. We agree with you, Dr. 
Frayne, that it would be a good idea to improve our printers as they stand today. 



Color-Television Film Scanner* 

BY BERNARD ERDE 

COLUMBIA BROADCASTING SYSTEM, NEW YORK 22, NEW YORK 



Summary The transformation of moving color-film images into video 
signals is accomplished with the most faithful rendition when the pickup tube 
is of the continuous-cathode, or nonstorage type. This, however, imposes the 
limitation that the film motion, in the associated film scanner, be constant in 
velocity, rather than intermittent. In the color-film scanner of the 
Columbia Broadcasting System, the pickup tube is the Farnsworth daylight 
image dissector. An optical-electronic method, requiring no moving optical 
parts, is used to compensate for the continuous motion of the film. 

THE COLUMBIA Broadcasting System postwar system of color tele- 
vision was put into operation in January of 1946. At first, the 
color-television pictures had their origin in 16-mm color film and 2-X 
2-inch color slides. In the spring of the same year, the live pickup 
camera and equipment were completed and put into use. 

Commencing with a brief review of the basic characteristics of the 
entire system, the remainder of this discussion will concern itself with 
a description of the methods involved and problems encountered in 
scanning the color film and slides. Particular attention will be paid 
to the design and function of the optical, mechanical, and electronic 
equipment involved in the process of transforming moving color-film 
images into video signals. 

The fundamental property of the system is one of sequential, 
additive-color scanning, in which the subject matter is analyzed into 
three primary-color impulses of varying amplitudes following each 
other in sufficiently rapid succession to be integrated by the observer's 
eyes. Rotating color disks, one in front of the pickup device and one 
in front of the receiving tube, properly synchronized and phased, 
produce the color analysis at the transmitter and the color synthesis 
at the receiver. The color images are scanned horizontally in 525 
lines, interlaced 2 to 1, and interlaced fields are scanned vertically at 
the rate of 144 per second. Each field, of Vi44-second duration, is 
scanned and reproduced in succession through a different primary- 
color filter, so that the three color fields are presented to the viewer 
in y 48 of a second, a sufficiently short interval of time to allow the 

* Presented May 10, 1946, at the SMPE Convention in New York. 

OCTOBER, 1948 JOURNAL OF THE SMPE VOLUME 51 351 



352 ERDE October 

eye's property of persistence of vision to give an apparent fusion of 
the separate colors into their resultant additive mixture. 

The film pickup tube is the Farnsworth image dissector with a day- 
light photoelectric characteristic. Its property of nonstorage photo- 
emissivity makes the dissector particularly suitable for color use, 
since there is no stored charge on the unscanned interlaced lines to be 
carried over from one color field to the next to produce spurious color 
values. Another distinct asset is its inherent freedom from shading 
effects. These two important characteristics of the daylight dis- 
sector account, to an enormous degree, for its fidelity of color 
rendition. 

The light source is a Peerless Hy-Candescent high-intensity carbon 
arc operated at 175 amperes. This is necessitated by the low sen- 
sitivity of the dissector and by the transmission loss in the color 
filters. Although the daylight dissector has been especially adapted 
for color work by improved response in the visible spectrum, it still 
has appreciable sensitivity in the near infrared. Since the red, blue, 
and green filters transmit freely in the infrared, this unwanted 
radiation must be removed by suitable filters if color contamination 
is to be avoided. A water cell containing a disk of heat-absorbing 
glass of the desired characteristic is inserted in the carbon-arc beam 
between condenser and gate aperture and is effective in transmitting 
a high ratio of visible light to total radiant energy. For valid color 
reproduction it has been found that the proportion of infrared 
response must not exceed more than 5 per cent of the maximum signal 
in the dissector output. However, since dissector tubes vary some- 
what in their spectral response, provision has been made to insert 
elsewhere in a cooler part of the light beam an additional heat filter, 
if necessary, to bring the infrared content below the permissible 
maximum level. 

OPTICAL SYSTEM 

Of greatest interest, perhaps, will be the optical system. Before 
describing this, it may be well to discuss first the factors instrumental 
in determining the choice of system to be used. 

The image dissector, as has been mentioned before, is a tube with an 
instantaneous photoemissive, or nonstorage, type of cathode. As such 
it imposes one basic limitation upon the type of projection equipment 
to be used with it; that is, the film cannot be intermittently projected 
upon the cathode. This restriction is caused by the shortness 



1948 COLOR-TELEVISION FILM SCANNER 353 

of the vertical blanking interval; Vi44o of a second. Whereas, with a 
storage type of tube the film can be projected during this short 
interval of time and then at relative leisure be pulled down in the film- 
gate aperture during the remaining 9 /i44o of a^second, with a dissector 
tube the film would have to be treated in the converse manner, 
i.e., projected during the 9 /i44o of a second scanning period and then 
pulled down during the 1 /i44o of a second blanking period. This, 
considering the masses and acceleration of the film and pulldown 
mechanism involved, is an impracticably short period of time and 
obviously rules out all consideration of intermittent projection. 

There are several well-known methods of continuous projection 
some of which have undoubted merit. l > 2 All involve the use of one or 
more optical elements, i.e., lens, mirror, or prism, actuated or driven 
by cam, wheel, or drum, to compensate for the displacement of the 
continuously moving film. It was felt desirable to avoid the use of a 
number of precisely adjusted optical elements driven by precisely 
machined mechanical members. It was also felt that most of the 
optical errors inherent to these types of optical displacement com- 
pensation, or inherent to the means employed to actuate them could 
be avoided. A method of optical compensation was employed which 
had earlier been used successfully at CBS in the transmission of 
black-and-white film. 3 The optical elements are six in number and 
consist of segments of simple achromatic doublets. They are entirely 
stationary, easily adjusted, and remain permanently fixed in position. 
The only rotating component is purely mechanical in function a 
rotating slotted selector disk which exposes the lens segments one at a 
time. Since the electronic scanning process, as will be pointed out, is 
also instrumental in offsetting the movement of the film, this may be 
termed an optical-electronic method of film-movement compensation. 

Since the film is moving at the rate of 24 frames per second and must 
be scanned at the rate of 144 per second, it is apparent that each frame 
must be scanned six times. This means that each frame will be com- 
pletely scanned as it moves a distance equal to one sixth of the per- 
foration pitch. ' Fig. 1 is a simplification of the action that takes place. 

The heavy arrows represent frame A occupying successive positions 
after each YJW of a second interval as it moves down through the gate 
at constant linear velocity. (For the sake of clarity the arrows are 
shown slightly displaced to the right in each position.) At the start, 
frame A is in position 1 in the- top of the gate, its lower five sixths (the 
heavier portion of the arrow) exposed. After l /u of a second it has 



354 



ERDE 






October 




1948 COLOR-TELEVISION FILM SCANNER 355 

moved to position 7 in the lower part of the gate, and has been scanned 
six times in the interim; frame B now stands in position 1 ready to 
repeat the cycle. It will be seen from the diagram that the height of 
the gate aperture must be equal to ! 2 /3 times the perforation pitch. 

Corresponding to each of these six positions of the frame in the gate 
is one of six lens-segment projection elements. These lens segments are 
arranged in a common plane normal to the main optical axis, with 
their centers in a straight line parallel to the direction of travel of the 
film. Each lens is so adjusted that it lies on the straight line joining 
the center of the scanned area on the cathode with the center of the 
lower five sixths of the frame in each position in the gate. In effect 
then, these lens segments are projecting upon the cathode sucessive 
overlapping images of the gate aperture, each displaced by an amount 
equal to one sixth of the perforation pitch. If, now, each lens segment 
is exposed alone for the time during which the frame is moving across 
the corresponding part of the gate, it will project upon the common 
scanned area of the cathode an image of the frame moving upward 
one sixth of the perforation pitch in l /m of a second. This moving 
optical image can then be scanned by deflecting its corresponding 
electronic image in an opposite direction over the physical scanning 
aperture at the other end of the dissector tube. 

It should be borne in mind that the optical image on the cathode is 
not stationary, but is moving upward for one sixth of the perforation 
pitch, repeating this for every vertical scanning period over the identi- 
cal portion of the cathode. The effectual immobilization of the image 
i is brought about by the action of the vertical scanning in a direction 
opposite to the image movement, i.e., the over-all vertical scan is the 
; resultant of one sixth upward motion of the image and five sixths (or 
i less) downward motion of the electronic scanning. The expression 
"or less" is used here because it is obvious that a resultant vertical 
scan of one perforation pitch is a little more than is usually desired 
I and would allow the frame line to be seen. In practice, the verti- 
; cal-scanning amplitude is adjusted to a value slightly less than five 
sixths of the magnified perforation pitch (more exactly, five sixths 
of the perforation pitch less the difference between the perforation 
pitch and the standard projector gate aperture height) to give a 
scanned picture height equivalent to the standard projector gate 
aperture height. 

Because of the geometry of the optics wherein six points spaced 
0.050 inch apart (this is equal to one sixth of the perforation pitch of 



356 ERDE October 

0.300 inch) are focused to a common point, it is obvious that the six 
projection-lens elements would have to be extremely small to avoid 
mutual physical interference. In practice, a standard projection lens 
is employed to form an enlarged virtual image of the gate aperture, so 
that the center-to-center spacing of the projection elements now be- 
comes of practicable dimensions. This is shown in Fig. 2, where for 
clarity, a simple plano-convex lens replaces the standard projection 
lens. In this diagram, a frame is shown in the No. 2 position in the 
gate with its enlarged virtual image projected through the No. 2 lens 
segment upon the scanned cathode area. The No. 2 lens segment is 
exposed through one of six slits in a rotating selector disk. These 
slits are concentric, adjacent arcs of 60 degrees and of differing radii, 
so that each slit exposes its associated lens segment at the proper time. 
The selector disk is driven at 24 revolutions per second by a syn- 
chronous motor, thus exposing the six lens segments in order every 
x /24 of a second. Since the selector disk must be synchronized with 
the film movement in order to have each lens segment exposed at the 
appropriate time, the motor frame is mounted so that it may be 
phased manually. 

The size of the selector disk is determined by the ratio of blanking- 
to -total-vertical-scan period; in this case, 1 to 10. Therefore, if the 
radius of the innermost slit is made such a value as to give the slit a 
length equal to 10 times the lens segment effective aperture length, 
the optical change-over will occur wholly within the blanking period. 
Allowing for the radial increments of the five other slits plus a small 
guard rim, the selector disk is 29 inches in over-all diameter. It is 
completely enclosed within a housing, and driven by a V4-horsepower, 
3-phase, 1800-revolution-per-minute synchronous motor, through 
a 5-to-4 reduction gear box, with complete absence of vibration. This 
latter point is of importance where extremely fine optical registration 
is to be maintained. 

LENS SEGMENTS 

The derivation of the lens segments may be understood by refer- 
ence to Fig. 3. Each segment is originally a fully formed, cemented 
achromatic doublet of 14-inch focus and l 3 / 4 -inch diameter. From 
each, the limb on each side of the optical centerline is cut or ground 
away until a segment of the desired thickness remains. It is evident 
that these lens segments of rectangular aperture will transmit more 
light than equivalent circular lenses of small-enough diameter to 



COLOR-TELEVISION FILM SCANNER 



357 




358 



ERDE 



October 



maintain the same spacing. The maximum lens segment center-to- 
center spacing for the optical constants involved is about 0. 140 inch. 
Allowing 0.010 inch between segments for adjustment purposes, 
this would leave a narrow, fragile piece of glass only 0.130 inch thick, 
if the lens were cut symmetrically with respect to the optical center- 
line. However, by cutting the lenses unequally on each side of the 
optical centerline, it is possible to maintain the same center-to-center 
spacing of the segments while at the same time materially increasing 
their thickness. This is shown on the right of Fig. 3 where the degree 
of asymmetry increases progressively with the distance of the lens 
segment from the common centerline. By this means the lens thick- 
ness has been increased to 0.160 inch, thus imparting a sturdier quality 



VERTICAL CL 





'OPTICAL CL- 



6 NARROW SYMMETRICAL 
SEGMENTS SPACED FOR 
GIVEN M" BETWEEN 
OPTICAL CENTER LINES 



6 THICKER ASYMMETRICAL 
SEGMENTS SPACED FOR 
SAME "d" 



LENS SEGMENT CUT FROM ENTIRE 
ACHROMATIC DOUBLET 

Fig. 3 Derivation of lens segments. 

to the segments, and more important still, increasing their light trans- 
mission by about 20 per cent. In addition to their strongly asym- 
metrical cut, as shown, the top and bottom segments, not being as con- 
fined as the interior ones, actually are about 50 per cent thicker in 
order to allow them to transmit still more light and thus improve the 
average signal-to-noise ratio. 

Since the six lens segments are to form six superimposed congruent 
images, it is necessary, for the sake of good resolution, that their real 
magnifications match very closely. Since the real magnification is 
closely dependent upon the focal length, this parameter must be 
controlled carefully in manufacture if satisfactory coincidence of 
images is to be obtained. 



1948 COLOR-TELEVISION FILM SCANNER 359 

If it is assumed that the images are to agree in size within 1 /z of a 
picture-line pitch, and if the centers of the images are made to coincide 
exactly, then the greatest disagreement will be at the extreme top (or 
bottom) where the picture lines will fall within */4 of a picture-line 
pitch, which is quite satisfactory. For a 500-line picture, a tolerance 
of */2 of a line pitch is equivalent to a tolerance in the magni- 
fication of 0.1 per cent. In this instance, the focal length is 14 
inches and the real magnification is 0.43 times. From the funda- 
mental relationship among focal length, magnification, and image 
distance, the permissible variation in focal length turns out to be 
0.010 inch, or a percentage variation of 0.08 per cent. This can 
be achieved in good optical practice. 

Three other properties required of the lens segments for satisfactory 
coincidence of images are freedom from curvature of field, negligible 
distortion, and good color focus. Curvature of field is reduped to a 
negligible minimum by good design aided by the long focal length and 
narrow angle of projection (a maximum of 2 degrees for the top of a 
frame entering the gate aperture, or the bottom of an exiting one). 
Distortion has been found to be almost entirely a function of the 
projection lens forming the virtual image. A high-quality projection 
lens will introduce no noticeable distortion. If the projection lens is 
also well corrected for color and if the lens segments have been achro- 
matized for the C and F lines, the color focus of the combination is 
found to be entirely satisfactory. In addition, the projection lens 
should have a wide aperture to avoid vignetting of the upper and 
lower frame images. The Bausch and Lomb //2, 4 1 /2-inch focus Super- 
Cinephor lens has been found satisfactory in all the above respects. 

In order to realize fully the accuracy with which the lens segments 
are fashioned, it is necessary that they be mounted in such a manner 
that they may be carefully adjusted for accurate optical alignment 
and then rigidly and permanently fastened in place. A mounting relief, 
Vie of an inch deep, ground into the ends of the segments, is utilized 
for fastening. Fig. 4A is a view of the lens-segment mount in posi- 
tion, with the selector disk shown behind. A sturdy brass aperture 
plate forms the basis of the mount and an arrangement of small 
metallic holding members and screws permits the individual segments 
to be adjusted vertically and horizontally and then clamped rigidly 
in place. 

The actual alignment of the lens segments is accomplished in the 
following manner. A reel, or loop of film, of a suitable geometric 



360 ERDE October 

resolution pattern is run through the scanner with the selector disk 
properly phased, and the resolution pattern is reproduced upon the 
picture monitor. In front of the lens segments, a slotted aperture 
frame (shown in Fig. 4B) receives masks containing rectangular 
apertures of different sizes and combinations so that the lens segments 
may be exposed singly or in combination. First, the No. 4 lens, 
lying just below the optical axis of symmetry, is exposed and the 
dissector electronic equipment is adjusted for normal picture- 
scanning amplitudes and optimum electronic focus. Then the dis- 
sector optical focus is adjusted by longitudinal racking of the dis- 
sector-tube mount until the image seen upon the picture monitor is 




Fig. 4 A Lens segment mount in posi- Fig. 4B Aperture frame and fixed, 
tion. ' segmented, tricolor filter. 

in best focus. The dissector tube is left in this position during the 
remainder of the alignment while each lens segment is adjusted in 
turn with respect to the No. 4 lens segment so that the images 
exactly coincide. By this method, coincidence of the six images can 
quickly be obtained to within a fraction of a line pitch in both the 
horizontal and vertical directions. 

The light efficiency pf the optical system is unavoidably low, since 
the//2, 4 1 / 2 -inch focus projection lens is in effect stopped down by the 
six lens segments to an average rectangular aperture of 0.180 X 1.375 
inches. The diameter of the equivalent circular aperture is 0.560 inch. 
Since the front element of the projection lens is almost completely 
filled with light and since the light beam has diverged only slightly 
when it falls upon the lens segments, the effective relative aperture of 



1948 COLOR-TELEVISION FILM SCANNER 361 

the complete system may be considered to be the ratio of 4.5 inches to 
0.56 or about //8. 

Nevertheless, despite the light lost in heat and color filtering as well 
as through the restrictive lens segments, the light flux incident upon 
the scanned portion of the cathode, an area equal to I 1 / 2 X 7 /s inches, 
is in the order of 4 lumens. This is sufficient to give a signal having 
an acceptable signal-to-noise ratio. 

Fig. 5 is a schematic view of the entire optical system. Here are 
shown the carbon-arc source, condenser, water cell, and heat-absorbing 
filter. Following these in order are the components of the film- 
scanning portion negative field lens (to be explained later) film gate, 
projection lens, optically polished auxiliary heat filter, selector disk, 
lens segments, a fixed segmented tricolor filter, and the dissector tube. 
It will be noted that there is no rotating color disk in this portion of 
the film-scanning optical system. In its place and performing the 
identical function of inserting sequentially in the light beam the three 
primary-color filters, the fixed segmented tricolor filter is used. This 
can be done because the lens segments are exposed sequentially ,and 
are six in number while the primary colors are three in number. Thus 
each lens segment is associated with a given primary color w^hich it is 
called upon to transmit to the exclusion of the other two primary 
colors. The color order of the lens segments from top to bottom is 
green, red, blue, green, red, blue. The fixed tricolor filter consists of 
six rectangular strips of green, red, and blue Wratten gelatin filter 
arranged in the corresponding color order and cemented between two 
squares of optically polished glass. This composite filter is held in 
place by means of a fixed aperture plate, close to the lens segments, so 
ithat each segment transmits its own associated color. The three 
primary color filters are green No. 58, red No. 25, and blue No. 47. 
In Fig. 4B, the tricolor filter is shown in place over the lens segments, 
with the individual colors somewhat indistinguishable in a black- 
and-white photograph. 

For color-slide projection a 45-degree plane, chromium-plated 
mirror is swung into the arc beam in front of the water cell to deflect 
the light through the slide-projection components. An auxiliary 
condenser lens, another 45-degree mirror, and a field lens serve to relay 
the arc beam and illuminate the aperture of the 2- X 2-inch slide 
carrier. From this point the light passes through another optically 
polished heat filter and then through the color filters of a synchronously 
rotating tricolor disk. The filters are six in number and arranged to 



362 



ERDE 




1948 COLOR-TELEVISION FILM SCANNER 363 

give exposure in the red, blue, green order. The disk rotates at 1440 
revolutions per minute so that each filter exposes the beam for Vi44 of 
j. a second. A Kollmorgen 8-inch-focus projection lens projects the 
slide image onto the cathode of the dissector tube which can be moved 
over to line up with this new axis of projection. Whenever a black- 
and-white image is needed for test purposes, an auxiliary light source, 
using a 500-watt incandescent lamp and condenser, can be cut in by 
swinging out the second mirror. Since the color disk is not needed 
for this latter purpose, a hinged mounting on the disk-and-drive 
structure permits it to be swung aside out of the light path. 

FILM-SHRINKAGE COMPENSATION 

As with all types of continuously moving film projectors, some 
; method must be employed to compensate for film shrinkage. The 
I necessity for this is evident upon consideration that the distances 
; between the centers of the six lens segments in the vertical direction 
have been permanently fixed and correspond to certain definite 
distances between the centers of successive frame positions in the 
gate. For another film, of less or greater shrinkage, these centers of 
successive frame positions will no longer correspond with the fixed lens 
segments, center-to-center distances, with the result that the super- 
; imposed images, although still remaining in sharp focus, will no longer 
coincide. To restore this coincidence of images, it is necessary only 
to refocus the //2 projection lens slightly in or out, and thereby 
diminish or enlarge the virtual image of the frame just sufficiently to 
realign the successive virtual frame position centers with their corre- 
sponding lens-segment centers. This adjustment, while restoring co- 
1 incidence, also alters the focus, which, however, is regained by shift- 
) ing the real image plane, i.e., the dissector tube, longitudinally. The 
! > result is exactly coincident and sharply focused images for any degree 
[ of film shrinkage encountered. 

Published data 4 and our own experiences have indicated that a 
range of to 1.5 per cent shrinkage should be accommodated. The 
; projection-lens barrel is calibrated directly in film shrinkage over this 
range, for both the standard and the nonstandard emulsion positions. 
| Calibration practice consists in making the initial lens-segment- 
spacing adjustment, which has already been described, with a test 
film of measured shrinkage in the gate. This shrinkage is then 
marked on the lens barrel opposite a fixed reference point. Several 
other test films of different shrinkages are then run through the 



364 



ERDE 



October 



scanner, and for each the projection lens is focused and the dissector 
mount readjusted to give an image on the picture monitor tube hav- 
ing the sharpest focus and the best coincidence. Each shrinkage set- 
ting is marked on the lens barrel and the determination of four such 
points is sufficient to allow a smooth curve to be drawn for the inter- 
polation of additional shrinkage settings. 

In operation, the shrinkage of the film to be run is measured before 




Fig. 6 Side view of film scanner. 

threading and the projection-lens barrel is preset to the corresponding 
shrinkage. Then, while the film is being scanned, the dissector-tube 
mount is adjusted for best resolution of the monitor image, whereupon 
optimum image coincidence and focus are simultaneously achieved. 
Because the depth of focus of the projection lens combined with the 
lens segments (the real magnification is less than unity and thej 
effective aperture is //8) is large compared with the permissible shift | 
of the projection lens as far as image coincidence is concerned, small j 
changes of shrinkage in the body of the running film can be accommo- 
dated by a slight refocusing of the projection lens. This always brings 



1948 COLOR-TELEVISION FILM SCANNER 365 

the images back to exact coincidence leaving the focus substantially 
unchanged. 

Film shrinkage is most easily, and with sufficient accuracy, de- 
termined by measuring the length of a given number of sprocket 
holes with a scale and dividing by the number of frames to obtain the 
average perforation pitch. It is convenient to use 39 sprocket holes 
and a 30-centimeter scale. This makes actual counting of the sprocket 




Fig. 7 Film scanner and dissector electronic scanning equipment. 

holes unnecessary, since the 39th hole will always fall between 293 and 
297 mm for a to 1.5 per cent shrinkage range. The measurement 
can then be left in millimeters per 39 frames, or transformed to per cent 
shrinkage by subtracting from and dividing by 297 mm, the nominal' 
length of 39 frames of unshrunk film. 

FILM-DRIVE MECHANISM 

Figs. 6, 7, 8, and 9 are views of the complete scanning equipment. 
On the left of Fig. 6 is the front of the arc lamp containing the water 
cell. In the center is the film-drive mechanism, and associated with 



366 



ERDE 



October 



it the upper and lower reel holders, projection lens, selector disk and 
lens-segment housing, selector-disk drive and manual phaser, and the 
control panel. On the right is the dissector-tube housing containing 
the tube and the scanning and focusing coils. The small knob 
beneath the dissector mount in Fig. 7 is for optical focusing and moves 
the tube mount longitudinally. The table-type rack beneath the dis- 
sector mount contains the electronic equipment for operating the dis- 
sector, namely, power supplies, scanning generators, and associated 
equipment. 




Fig. 8 Front view of film scanner. 



Fig. 9 Slide-scanning components. 



Fig. 6 is of special interest in that it reveals the origin of the mech- 
anism for pulling down the film at a constant rate of speed. When 
design of the film scanner was first begun, serious consideration was 
given to the possibility of adapting some existing commercially 
available 16 T mm sound-film projector to television-film scanning. Of 
several models examined with this end in view, the Ampro Premier No. 
10 projector was selected as being the most conveniently adaptable 
from the constructional standpoint. The soundhead assembly was 
retained in its original form while the rest of the projector was modi- 
fied by removing the intermittent pull-down mechanism, the shutter 
drum, and the motor drive and blower. Only that portion contain- 
ing the pull-down and take-up sprockets and the associated gear train 



1948 



COLOR-TELEVISION FILM SCANNER 



367 



was retained. Around this as a nucleus, the rest of the film drive 
was designed. 

As shown in Fig. 6, a Maurer precision sprocket for constant-speed 
film drive is built in just underneath the film gate. This sprocket is 
driven through a mechanical filter consisting of a 10-inch flywheel, 
spring coupling, and suitable damping. These are shown in Fig. 10, 




Fig. 10 Mechanical filter for constant-speed 
sprocket. 

which is a top view of the scanner with covers removed. Although 
the speed of the sprocket is low, being only 3 revolutions per second, 
the mechanical filter is extremely efficient in smoothing out any fluc- 
tuations in the drive that might tend to be imparted to the film 
motion, and the images are gratifyingly steady. The inherent 
24-cycle-per-second sprocket modulation normally introduced by the 
sprocket teeth has been minimized by suitable sprocket design, and 



368 ERDE October 

there is no observable impairment of optical resolution from this 
source. 

The motive power is furnished by an 1800-revolution-per-minute 
synchronous motor coupled to the constant-speed sprocket assembly 
through a 1 : 1 right-angled spiral gear drive and a 10 : 1 worm and 
worm gear. A motor-shaft extension engages directly with the Ampro 
gear train to drive the pull-down and take-up sprockets. This 
arrangement effectively isolates the constant-speed sprocket behind 
its mechanical filter and frees it from any motional irregularities intro- 
duced by the remainder of the mechanism. For picture framing, the 
motor shell can be rotated manually in its support by means of a long 
shaft and a knob located conveniently on the front of the scanner. 

Also shown in Fig. 10 are some of the components of the slide 
projection system, the auxiliary condensers, slide holder, color disk 
and drive, and the stand-by incandescent-lamp source. An air blast 
for cooling the film and slide gates and the dissector tube is obtained 
from a central blower beneath the scanner and linked to those points 
through manifold and air-hose connections. 

FLICKER 

The nicker to be discussed here at length is that which has its 
origin in the optical characteristics of the film-scanning system and 
not the flicker arising as a function of the field-repetition rate and 
the brightness level at the receiver. 

Regarding the latter, however, this much will be mentioned as of 
general interest. The CBS prewar system of color television was 
based on a field repetition rate of 120 per second. This permitted a 
high-light brightness at the receiver of 2 foot-lamberts for just per- 
ceptible flicker. Postwar investigations indicated the desirability of a 
higher field-repetition rate, and when this was raised to the present 
144 per second, a high-light brightness at the receiver of 9 foot- 
lamberts was obtained. Subsequent changes in receiver-filter 
characteristics have enabled the receiver-flicker threshold to be 
raised to a value of 20. foot-lamberts. 

It might seem, from a review of the basic optical design of this type 
of film scanner, that flicker would be rather a vexing problem. This 
conclusion might, quite naturally, be drawn upon consideration of two 
innate characteristics of the optical system. First, successive images 
of a frame in successive portions of the film-gate aperture are, in effect, 
superimposed in projection on the photocathode. Should the gate 



1948 COLOR-TELEVISION FILM SCANNER 369 

aperture be nonuniformly illuminated, corresponding areas of the 
image may go through a cyclic variation in brightness and cause a 24- 
cycle-per-second regional flicker. Second, in performing their 
function of consecutively projecting a frame as it occupies different 
portions of the gate aperture, the lens segments must suc- 
cessively select different portions of the cross-sectional area of the 
light beam. If the light beam is nonhomogeneous, or if one of a pair 
of lens segments transmits light unequally, again there may be a 
periodic variation in the brightnesses of the superimposed cathode 
images, evidencing itself this time as an over-all 24-cycle-per-second 
flicker. (The lens segments are paired in the sense that the first and 
fourth are filtered to transmit only green light; the second and fifth, 
red light; and the third and sixth, blue light.) 

It follows then, that the solution of the flicker problem depends 
upon two requirements. First, that of securing adequately uniform 
distribution of illumination in the gate aperture over its full height 
(equal to approximately 10/6 X perforation pitch of 16-mm film, or 
0.500 inch) and second, that of obtaining equivalent transmissions of 
light through both lens segments in a pair. 

The first requirement, that of adequate uniformity of gate- 
aperture illumination, is fairly easily met by the fact that the 16-mm 
gate-aperture dimensions (even though extended of necessity to 0.500 
inch in the vertical direction) are less than those of a 3o-mm film 
aperture, for use with which the arc-lamp condenser was designed. 
In addition, a negative field lens (whose function is of greater impor- 
tance in enabling the second requirement to be met) behind the gate 
aperture permits a more enlarged crater image, so that by proper re- 
focusing of the arc condenser a compromise between light intensity 
and light distribution can be effected in which the gradient of illumi- 
nation from the center of the aperture upward and downward is not 
large enough to introduce any regional flicker as the images of a 
frame in the different gate positions coregister on the cathode. 

The second requirement, that of obtaining equivalent transmissions 
of light through both lens segments in a pair, too, has not offered 
great difficulty. The negative field lens inserted behind the gate 
aperture has a focal length of 145 mm. The effective focal length of 
the combination of this lens 1 with the 4 1 /2-inch-focus projection lens 
is such as to project into the plane of the six lens segments a reduced' 
image of the front surface of the forward arc-lamp condenser lens, and 
of a circumference closely circumscribing the total rectangular area of 



370 ERDE October 

the six lens segments. Thus, while also insuring the maximum re- 
laying of light through the lens segments, the homogeneity of the cross 
section of the light beam in this plane is considerably improved. 
Although this would give substantially equal transmissions of light 
through lens segments of equal areas, it should be recalled that the 
top and bottom lens segments have been intentionally designed to have 
appreciably greater area than the other segments. As has been 
pointed out earlier, the top and bottom lens segments do not have the 
spacing restrictions that are of necessity imposed on the interior ones. 
Consequently, these outer segments have been made with a 50 per cent 
greater area in order to increase the average light transmission and 
thereby improve* the average signal-to-noise ratio. To exploit this 
situation fully, it is necessary that some means be employed to convert 
the repetitive light pulses of unequal level into resultant signal pulses 
of equal level. The mechanism to be described accomplishes this by a 
form of automatic gain compensation synchronized with the sequential 
exposure of the lens segments that permits the equalization of the 
magnitude of any pair of lens segments' light-to-signal conversion 
simply by adjusting the corresponding knobs on a control plane 
while the actual film-scanning process is under way. 

A rotating switch arm attached to a shaft rotating at the syn- 
chronous speed of 1440 revolutions per minute sweeps over six con- 
tacts fixed at the periphery of a manually adjustable disk. Each 
contact is connected to its own flicker-control potentiometer and the 
six potentiometers are shunted across a common stage of the elec- 
tron multiplier in the dissector tube. With the equipment in oper- 
ation but with no film in the gate, with the selector disk running and 
light falling through the lens segments to focus the gate-aperture image 
on the cathode, the contact disk is phased by hand until the switching 
change-over falls wholly within a vertical blanking period (as shown 
upon either the wave-form or the picture monitor) and is then clamped 
permanently in place. It can be seen that the gain of the multiplier 
stage during a given color field now will depend upon the resistance of 
only that potentiometer which is connected across it for the du- 
ration of that color field. 

If the wave-form monitor sweep frequency has been adjusted to give 
three color fields, it will be noted that each color field consists of two 
fields superimposed (two green, two red, and two blue). Since each 
of the six flicker-control potentiometers affects the level of its 
corresponding color field only, it is then a comparatively simple 



1948 COLOR-TELEVISION FILM SCANNER 371 

matter, while observing the wave-form monitor, to adjust the paired 
color-field amplitudes until the two components of each pair are 
equal and at a maximum, whereupon equal and maximum signal am- 
plitudes for the paired lens segments of each color will have been 
derived. For slide transmission, the flicker-control potentiometers 
are switched off since they need not then, of course, be used. Once 
this adjustment has been made, no further flicker adjustment is 
thenceforth necessary, barring excessive maladjustments in the 
carbon-arc trim or condenser alignment. 

Color mixing is accomplished in a somewhat similar manner, with 
the difference that the response through both of a pair of lens segments 
(instead of through each individual lens segment) is varied simul- 
taneously and automatically. Color mixing means, simply, vary- 
ing the ratios of red-to-blue-to-green signal levels. Although the 
color-filter chromaticity and transmission values have so been 
selected that normal color reproduction (with also the widest pos- 
sible range of colors and color saturation) will be obtained when the 
red, blue, and green signal levels are equal, there often arises the need 
for altering these ratios either to achieve a more pleasing effect or to 
compensate for color-balance deficiencies in the film. A second 
rotating switch arm attached to the flicker-control switch arm 
shaft and space-phased to it sweeps in like manner over six contacts. 
These six contacts are connected diametrically in pairs and each pair 
is connected to its own color-level-control potentiometer. 

The three color-level-control potentiometers are shunted across a 
second common stage of the dissector-tube electron multiplier. When 
proper phasing has been obtained the levels of the red, blue, and green 
signals can be varied independently from zero to a maximum simply 
by turning the corresponding knob on the color-control panel. 

Other controls on the color-mixing panel include the usual bright- 
ness-level control, a master gain control which varies the red, blue, 
and green signal levels simultaneously without altering their ratios, 
and a gamma-correction control for varying the contrast distribution 
of the entire system. 

An interesting feature of the film scanner is that it is not uniquely 
a color-television standards device. Provision, in fact, has been made 
for a quick change-over in a matter of minutes from color to the Radio 
Manufacturers Association standard black-and-white transmission. 
Should that be desired, it is only necessary to replace the six lens 
segments holder with one containing five lens segments adjusted for a 



372 ERDE 

VB perforation-pitch interval of 0.060 inch of a center-to-center spacing 
of 0.168 inch. The six-slit selector disk is also replaced with one 
containing five slits arranged in a 1, 3, 5, 2, 4 order (instead of the con- 
secutive order as in color transmission) . Then with the gear-box trans- 
mission shifted to 720 revolutions per minute the selector disk rotates 
at the proper speed to allow a frame to be projected and scanned, as it 
moves 2 /o of a perforation pitch, in 1 / M of a second, giving 5 scans of 2 
frames in 1 /i 2 of a second, or 60 fields per second. 

Although the foregoing description may have created an impression 
of delicacy and complexity in the function of the CBS color-tele- 
vision film scanner, it must be emphasized, in concluding, that in 
two and one half years of constant use, this film scanner has 
given quite definite proof of the practical nature of its design. 
During this time it has given dependable and consistently satis- 
factory results as a transformer of moving color-film images into 
video signals, with no more than the normal amount of operating 
adjustment and maintenance required of any piece of studio equip- 
ment. Several similar scanners have since been built, and in every 
case the requisite optical, mechanical, and electronic precision and 
dependability have been easily reproduced. 

REFERENCES 

(1) Fordyce Tuttle and Charles D. Reid, "The problem of motion picture pro- 
jection from continuously moving film," J. Soc. Mot. Pict. Eng., vol. 20, pp. 3-31 ; 
January, 1933. 

(2) F. Ehrenhaft and F. G. Back, "A non-intermittent motion picture projec- 
tor," /. Soc. Mot. Pict. Eng., vol. 34, pp. 223-232; February, 1940. 

(3) Peter C. Goldmark, "A continuous type television film scanner," /. Soc. 
Mot. Pict. Eng., vol. 33, pp. 18-26; July, 1939. 

(4) J. A. Maurer and W. Bach, "The shrinkage of acetate-base motion picture 
films," /. Soc. Mot. Pict. Eng., vol. 31, pp. 15-28; July, 1938. 



FORTY YEARS AGO 

The Future 

The future of the moving picture machine is a theatrical problem. 

Some theatrical men believe that it will prove a serious competitor of 
the vaudeville. They suggest the time when the phonograph will work 
with it, and the best act of the newest New York comic opera will be 
flashed on the screen and sung out of the phonograph. 

Others, and probably these are right, say that the picture machines 
have hit their highest notch. 

The Moving Picture World, January 4, 1908 






35-Mm Process Projector* 

BY HAROLD MILLER AND E. C. MANDERFELD 
MITCHELL CAMERA CORPORATION, GLENDALE, CALIFORNIA 



SummaryA studio type of process projector, designed and built to meet 
the specifications as set forth by the Motion Picture Research Council Com- 
mittee, is described. Both the single- and the triple-head projectors are 
discussed. 



THE MITCHELL background projector as supplied to most of the 
major studios is an outgrowth of a development originally 
started about 1934. Previous to this time, as well as during the period 
up to now, background projectors have been for the most part semi- 
experimental laboratory-type machines built up by studio technicians 
from various odds and ends available from the studio camera shop. 

The present projector design is based on the recommendations as 
stated in the Academy specifications entitled "Recommendations on 
Process Projection Equipment/ 7 published in February, 1939, by the 
Process Projection Equipment Committee of the Research Council of 
the Academy of Motion Picture Arts and Sciences. The Research 
Council report showed the need for process projection equipment that 
could be used on the sound stage without the use of blimps or portable 
projection rooms to contain the noise of the equipment, that would be 
portable on a suitable dolly and movable to various stages, that could 
deliver the maximum light possible with a modern optical system, and 
that could project an absolute steady picture. 

The following is a description of the various components that consti- 
tute the complete process projector which meets these requirements. 

PROJECTOR HEAD 

The projector head is composed of a vertical drive shaft and four 
driven cross shafts coupled by helical gears and held in accurate align- 
ment by oilite bearings. The cross shafts drive two 32-tooth sprock- 
ets, the movement, and the 180-degree rear shutter. This mecha- 
nism is enclosed in an invar steel housing, and is lubricated by grease 
of 2500 to 3000 viscosity through three Zerk fittings. The unit is 

* Presented May 18, 1948, at the SMPE Convention in Santa Monica. 

OCTOBER, 1948 JOURNAL OF THE SMPE VOLUME 51 373 



374 MILLER AND MANDERFELD October 

mounted in an aluminum case which is fitted with the necessary idler 
rollers to guide the film to and from the sprockets and the magazines. 
The Mitchell compensating link camera movement, Fig. 1, is used! 
in the head to provide pilot registration pins necessary for "rock- 
steady" projection. The movement is modified for process projection 
by placing the claw and operating mechanism below the aperture away 
from the light beam and heat. The removable back plate and register 
plate are open between the film tracks to release condensation of mois- 
ture from the film and to eliminate the possibility of scratching. The 
movement is provided with an adjusting screw to adjust for shrinkage, 

and also to adjust for minimum 
film noise while running both 
forward and backward. 

The movement is coupled to 
the head by a key coupling 
which can be engaged in only 
one position thereby insuring 
that the movement is in time 
with the shutter. The movement 
position is set by a dowel pin 
to keep the necessary alignment 
between aperture and optical ele- 
ments, and is locked in place by 

w" t -D.-' thumbscrew clamps. A dummy 

Fig. 1 Projector movement. 

aperture is used in place of the 

movement to align the optical system and check screen illumination. 
Both movement and dummy apertures accommodate mattes of 
Academy and Standard apertures. 

UPPER AND LOWER MAGAZINES 

As shown in Fig. 2, the upper magazine is mounted on top of the 
head and the lower magazine bolts to the back of the head. The 
magazines are 13 inches inside diameter, giving ample hand room 
when using 1000-foot -reels or spools. They are lined with corduroy- 
velvet for protection to the film. The magazine doors are fitted with 
8-inch windows, thereby providing a full view of the film passing 
through the head. Both magazines are equipped with adjustable 
overriding clutch, felt friction disk take-up drives. Also there are 
adjustable pull-down brakes inside of the magazines to provide the 
proper film tension for running forward or backward. 




1 1948 PROCESS PROJECTOR 375 

LENS MOUNTING 

The lens mount bolts on to the front of the projector head. It has a 
} 5V2-inch diameter opening to accommodate //2.0 lenses from 4 to 8 
inches focal length. 

The lens mount is equipped with jackets to hold various focal-length 
lenses. The jackets are slipped in the lens mount and are held in place 
I by a retaining pin. The lenses are easily changed by lifting the knob 
I on the retaining pin, removing the jacket, and inserting another. 

The lens mount has a manual focusing knob at the operating side 
and a Selsyn receiver motor for remote control from the camera 
position. 




Fig. 2 Projector head and light tube. 



REMOTE-FOCUSING CONTROL 

The remote focusing of the objective lens on the background screen 
is practically standard procedure in most studios for several reasons. 
First, the correct focus position is that whereby the projected image 
looks best as viewed from the camera position. Second, while the set is 
being prepared for the next "take" it is quite customary for the light- 
ing crew to set up and test the various lights. This light, when falling 
on the background screen, for the most part, makes it difficult and at 
times practically impossible to see the image on the screen from the 
projector position. 

Several methods or means for remote focusing were considered. 
The method adopted was the use of Selsyn motors. Essentially it con- 
sists in interlocking two single-phase Selsyn motors, one of which is 



376 MILLER AND MANDERFELD October 

mounted as a receiver in a manner to actuate the focus of the projector 
objective lens, and the other one at the remote focusing point which is 
used as the transmitter. The latter motor shaft is provided with a 
small handle so it can be rotated manually in either direction and thus 
through the electrical interlock rotate the lens-actuating motor. 

The remote-focusing motor is encased in a housing having a con- 
venient handle for carrying the motor about on the stage. Because of 
its general appearance it is commonly referred to as the "beer mug." 
A push button is incorporated in the carrying handle which first must 
be pressed down in order to excite the two motors electrically. This is 
a safety device to prevent accidental movement of the projector lens 
by inadvertent movement of the "beer-mug" rotating handle. 

HEAD MOUNTING 

The complete projector head, magazines, and motor are coupled by 
means of a ring coupling to an aluminum casting, Fig. 2, commonly 
known as a light tube. This permits the projector to be revolved 
about its optical axis. An adjustable worm gear controls the rotation 
15 degrees each side of vertical. However, by rotating farther, there- 
by disengaging the worm from the gear, the projector head can be re- 
volved to any position within 125 degrees each side of vertical. The 
head is locked in place by a clamping screw on the coupling ring. 

The relay lens (described in more detail later), Fig. 3, is located in 
the light-tube casting behind the projector head. This unit is 
mounted with the necessary controls so that it can be adjusted hori- 
zontally, vertically, and axially for focus. The condenser lenses in the 
arc house have a similar set of controls. 

The relay lens holder is a hard, chrome-plated, aluminum casting 
and is provided with a 2-inch space between the two elements. This 
space is filled with boiled distilled water for the purpose of removing 
much of the heat in the condenser-light beam. 

To remove the heat from the distilled water, ordinary tap water is 
circulated in a hollow space around the periphery of the relay lens 
holder. This circulating water also passes through the cooling jacket 
in the Mole-Richardson lamp, then to a vertical flow-type radiator 
located under the lamphouse. The radiator unit includes a four- 
bladed fan driven by a 1 /4-horsepower, direct-current motor. This 
motor circuit is interlocked with the lamp control in a manner which 
makes it impossible to operate the arc unless the cooling fan is running. 



1948 PROCESS PROJECTOR 377 

The fan operates normally at 1700 revolutions per minute, but drops 
to a reduced speed when the projector driving motor switch is on. 
This procedure reduces the noise level during a "take." 

Also included in the radiator unit is a circulating-water pump direct- 
connected to a small alternating-current motor. This motor circuit is 
also interconnected in a manner to prevent the lamp from being oper- 
ated unless the circulating motor is operating. 




Fig. 3 Relay lens. 

CONDENSER OPTICAL SYSTEM 

For background projection work it is very essential that the screen 
illumination be adequate, uniform across the screen, and of the proper 
color quality. To achieve all three of these characteristics requires a 
somewhat more complicated optical system than normally used in 
theater projectors. 

In the development of our optical arrangement, the previous art on 
condenser systems as developed by Bausch and Lomb, Technicolor, 
Paramount, and others was investigated. From the literature cover- 
ing this art, it appears that the basic ideas underlying such optical sys- 
tems are not too new, and it seems that most of the recent improve- 
ment is due to more careful designing and the use of more precisely 
made optical parts. In Fig. 4, it may be seen that the Mitchell system 
makes use of a relay lens (already mentioned) used in conjunction with 



378 



MILLER AND MANDERFELD 



October 



a standard condenser unit with a collecting angle of nearly 90 degrees. 
An image of the arc crater is projected by the two-element condenser 
to an image point located at A . This enlarged image is again focused 
by means of the relay lens at a point B which in general is close to the 
rear surface of the projector objective lens. 

In transferring the crater image from point A to the objective lens, 
an interesting intersection of light rays takes place which is of prime 
importance to the quantity as well as the quality of the screen illumi- 
nation. Starting at point 3 of image A, three rays can be traced 
through the relay lens, through the film aperture and to point 3 of 
image B. It should be particularly noted that these three rays pass 




Fig. 4 Condenser-lens optical schematic. 

through the film aperture at the top, center, and bottom. In other 
words, the light emanating from point 3 of image A covers the entire 
area of the film aperture. If now a similar bundle or cone of light rays 
is traced from point 2 of image A to point 2 of image B, it will be found 
that as before this point radiates a light cone which covers the 
entire film aperture. Thus every point of the image plane A will indi- 
vidually cover every portion of the entire film aperture. The resultant 
effect is a uniform light intensity over the entire area of the film aper- 
ture regardless of the light uniformity of the image source at A. 

In tracing the light rays back from the image plane A to the arc 
crater, another interesting feature may be observed. Starting at point 
3 of image A it should be noted that the lower ray intercepts the larger 
condenser element very nearly at the rim and progresses through the 
other condenser element to the upper edge of the arc crater. The cen- 
tral ray from point 3 passes through the condenser element at a point 
approximately in the center, whereas the upper ray passes through the 







PROCESS PROJECTOR 



379 



denser element close to the outer rim. Thus point 3 of image A is 
for practical purposes illuminated from rays emanating from the entire 
surface of the condenser element. 

In a similar fashion, if one traces a series of rays from point 2 of 
image A to the arc crater one will find that the illumination of the cen- 
ter point of the image at A also depends on the entire surface of the 
condenser element. All this can be summarized by saying that this 
optical system is so designed that it will provide very uniform illumi- 
nation over the aperture area and in addition makes effective use of all 
the light that can be picked up by the condenser system. 

FIRE SHUTTER 

An automatic fire shutter, Fig. 
5, is located behind the relay lens 
in the light-tube casting, and is 
mounted from the top of the 
casting. The shutter unit is com- 
posed of a cast-Inconel dowser 
blade to withstand the heat of 
the light beam. A direct-current 
solenoid holds the shutter open 
when energized through a circuit 
controlled by the fire-shutter 
governor. The governor unit 
includes the necessary adjust- 
ments to operate the fire-shutter 
solenoid when the projector motor 
reaches 700-revolutions-per-friin- 
ute speed. It releases the shutter when the motor speed drops to 
600 revolutions per minute, thus protecting the film from the exces- 
sive heat of the arc. A handle is also provided for manually operat- 
ing the fire shutter, thereby enabling the projectionist to flash the 
light on the screen without the necessity of running the projector. 

A variable-light aperture of cast Inconel is mounted in the light- 
tube casting immediately behind the governor-controlled fire shutter. 
This aperture is controlled by an eccentric coupled to an operating 
knob on the outside of the light tube. An indicator dial is provided to 
allow accurate setting of the light aperture. 

Variation of the light aperture does not affect the uniformity of the 
light intensity on the film and therefore the arc carbons can be burned 




Fig. 



5 Variable aperture and fire 
shutter. 



380 



MILLER AND MANDERFELD 



October 



at the maximum amperage consistent with good operating efficiency 
and steadiness of light. 

ARC LIGHT 

The light source is a Mole-Richardson Type 250 arc lamp designed 
and built for the Mitchell Camera Company. The details of the con- 
struction and operation of this lamp have been covered in this JOUR- 
NAL for July, 1947, in a paper entitled "Recent developments of super- 




Fig. 6 Electrical control box. 

high-intensity carbon-arc lamps," by M. A. Hankins. As described 
in this paper, the lamp is used in conjunction with a ballast grid and 
automatically maintained at the proper operating position by a 
photoelectric control system, thereby insuring very constant operat- 
ing characteristics without the necessity of constant vigilance on the 
part of the projectionist. 

ELECTRICAL CONTROLS 

The electrical-control-circuit layout for the background projector is 
based on the general over-all requirements as requested by several 









1948 



PROCESS PROJECTOR 



381 



studios. In general, the circuit arrangement allows the projector to 
run either forward or backward in interlock, or "wild." In an emer- 
gency all the leads to the driving motor can be broken simultaneously. 
The actual switching is done by Leach relays which in turn are under 
control of heavy-duty snap switches. 

All electrical connections are brought into or out of the background 
projector unit by means of Cannon plugs. Consequently it is a rela- 
tively simple matter to replace complete assemblies or to disconnect 
power supplies for routine maintenance. All important circuits are 
supplied with fuses to eliminate 
the danger of equipment over- 
load. 

Mechanically, the various com- 
ponents of this electrical system 
are disposed as follows: 

All the electrical relays, fuses, 
rectifier, and the intercommuni- 
cation amplifier are located in a 
large metal box, Fig. 6, located 
just below the arc house and on 
the nonoperating side of the pro- 
jector. The snap switches used 
for controlling the various cir- 
cuits are located on the arc-light 
control panel on the operating side of the projector, Fig. 7. The 3- 
phase rheostat used for "wild" operation of the driving motor is also 
located on this pajiel. 




Fig. 7 Single-head projector. 



720-REVOLUTION-PER-MlNUTE OPERATION 

The photographing by means of a standard motion picture camera 
of an image projected from a background projector necessitates that 
the shutter on the camera be properly synchronized with the shutter 
on the projector both as to rotational speed as well as phase or instan- 
taneous angular position. 

Assume the use of 2-pole, 3-phase interlock driving motors on both 
the camera as well as the projector, both electrically coupled to a com- 
mon distributor. If the stators of the motors and the distributor are 
excited from a common 60-cycle, 3-phase power supply and all the 
rotor circuits are properly interconnected, each rotor will align itself 



382 . MILLER AND MANDERFELD October 

in some mechanical position so that electrically there is no transfer of 
power from any one rotor to either of the others. If one rotor is 
mechanically rotated or displaced to some new position, the other 
rotors will follow mechanically, in order to rebalance themselves 
electrically. 

If now the shutters of the camera and projector are mechanically 
aligned, while all the interlocked rotors are in electrical balance, it can 
readily be seen that if the distributor (assumed to be 4-pole) is rotated 
by means of a mechanically coupled driving motor, say at 720 revolu- 
tions per minute, the 2-pole interlocked motors will operate at 1440 
revolutions per minute, and both the shutters will rotate in synchro- 
nism as well as maintain their relative angular phase while rotating. 

Now it so happens that with a 2-pole motor there is only one 
mechanical alignment position for an electrical power balance of the 
rotor. With 4-pole motors there are two mechanical alignment posi- 
tions 180 degrees apart where the rotor can be electrically in power 
balance with the distributor. However, if the shutter shaft is coupled 
to a 4-pole driving motor by means of a 2-to-l gear unit, it will act as 
though it were coupled directly to a 2-pole motor. 

Practically, there is an advantage in using a 4-pole interlock driving 
motor for the background projector, namely, that of availability. In 
general, 2-pole interlock motors are available only for camera drives 
and, because of the small frame size and the low resultant power out- 
put, this type of motor was not considered adequate for driving the 
background projector and thus a 4-pole motor was used instead. 
Since the camera and projector shutters must both run at 1440 revolu- 
tions per minute, a 720-revolution-per-minute, 4-pole, or a 1440-revolu- 
tion-per-minute, 2-pole distributor has to be used. 

From the foregoing discussion it becomes rather apparent that the 
use of a 720-revolution-per-minute interlock driving motor electrically 
coupled to a 4-pole, 720-revolution-per-minute driven distributor 
always insures the proper shutter alignment after the initial adjust- 
ment. If some other .driving speed such as 1200 revolutions per min- 
ute were used, this would not be the case. 

It should be mentioned that the use of the 720-revolution-per-min- 
ute interlock motor-drive system for background projection use was 
not original with the Mitchell company. Several studios, notably 
Paramount and Warner Brothers, have used this method for interlock- 
ing for some years and therefore should be given due credit. 



1948 



PROCESS PROJECTOR 
SINGLE- AND TRIPLE-HEAD BASE 



383 



The projector head and associated lamp unit are so designed that 
they are interchangeable for either single- or triple-head assembly. 
The triple-head unit (Fig. 8) of course requires two reflecting mirrors 
for two of the three heads. This facility of being able to disassemble 
a triple head readily into three separate projectors greatly increases 
the range of activity for the process department. 




Fig. 8 Triple-head projector. 

The "dolly" base of the single-head projector provides "rocklike" 
stability when "locked off" for operation, and yet it can be easily 
moved about the stage by two men. The panning and tilting mecha- 
nism operates with smoothness and precision. 

Four solid-rubber-tired wheels are attached to the fabricated steel 
base of the single-head projector, Fig. 7. The rear wheels are 
mounted on swivels and hinged to the frame. They are connected by 
a tie-rod, enabling the base to remain level when moved over an 
uneven surface. 



384 MILLER AND MANDERFELD 



By means of a handwheel on the center column, the optical axis can 
be raised from 4 feet 9 inches to a height of 6 feet 3 inches. The col- 
umn is also equipped with a handwheel to pan over an arc of 180 de- 
grees. A third handwheel tilts the projector 12 degrees up or down 
from horizontal. 

In order to provide levelness and stability during the operation of 
the projector, the base is equipped with three screw jacks. 

The T-shaped base of the triple-head projector, Fig. 8, is constructed 
of fabricated steel, and equipped with solid-rubber-tired swivel wheels 
and screw jacks at each end of the T base. It is equipped with two 
handwheels to pan 22 degrees and tilt 11 degrees up or down from 
horizontal. The height of the optical axis of the three projectors on 
this base is 5 feet 6 inches when parallel to the floor. Both bases are 
equipped with removable tow bars. 

ACKNOWLEDGMENT 

In conclusion, the Mitchell Camera Corporation wishes to acknowl- 
edge the valuable help and suggestions made by the process depart- 
ment personnel of the various studios. In particular, we wish to 
thank Mr. Farciot Edouart and Mr. Hal Corl of Paramount Studios 
for their efforts in obtaining data of various sorts and for their techni- 
cal suggestions during the development of this process projector. 






FORTY YEARS AGO 

It is alleged that many of the moving picture theaters in this city are 
still having their machinery operated by boys under sixteen years of 
age, especially on the latter East Side. The scheme is said to be to have 
some matured operator go before the authorities and pass an examina- 
tion and then turn the license over to the youngster. The Board of 
Fire Underwriters and the Fire Department had better look into this 
and if found to be correct to lock the offending manager up, send the 
person who took the examination to Blackwell's Island and send the 
"kid" operator to the Reformatory. No punishment is too severe for 
people who conspire to do things that put human life in jeopardy. 

The Moving Picture World, May 80, 1908 



New Theater Loudspeaker System* 

BY H. F. HOPKINS 

BELL TELEPHONE LABORATORIES, MURRAY HILL, NEW JERSEY 

AND 

C. R. KEITH 

WESTERN ELECTRIC COMPANY, NEW YORK, NEW YORK 

Summary The new system employs sectoral high-frequency horns and 
a crossover frequency of 800 cycles. Improvement is obtained in uniformity 
of distribution and reduction of size and weight. 

4 LOUDSPEAKER SYSTEM of the excellence required for motion pic- 
JL\_ ture applications must be founded on sound fundamental prin- 
ciples, many of which are understood fully only as a result of a con- 
siderable background of experience in the field. Such a background 
must be established before the application of technical skill can be 
successfully applied to the development effort. Since the interpreta- 
tion of the basic principles is so important to the success of the ven- 
ture, it seems appropriate to discuss briefly the considerations upon 
which the new Western Electric loudspeaker designs were based. 
The description of the physical embodiment which follows later will 
then have greater significance. 

Before setting the course for a specific development of this type, 
many diverse and complex phenomena must be weighed, and the 
various merits and demerits of certain opposing characteristics must 
be reconciled. The following paragraphs will attempt to rationalize 
such a procedure. Where possible, data illustrating the effects dis- 
cussed as well as the performance of the final loudspeaker system will 
be presented. In order to simplify the discussion, the various general 
attributes of a loudspeaker will be considered individually, and their 
relation to practice defined. 

FREQUENCY RESPONSE 

It is quite generally agreed that one of the more important yard- 
sticks in the determination of loudspeaker performance is the fre- 
quency-response characteristic. In the development of speakers for 

* Presented October 24, 1947, at the SMPE Convention in New York. 

OCTOBER, 1948 JOURNAL OF THE SMPE VOLUME 51 385 



386 



HOPKINS AND KEITH 



Octob< 



any specific use, therefore, it becomes necessary to determine what 
response characteristic is needed to fulfill- the requirements of the situa- 
tion best. The employment of shaped, or "distorted" response to 
provide certain desirable characteristics such as high intelligibility in 
the presence of high ambient noise is well known. The commonly 




Fig. 1 Arrangement of horn and loudspeaker for outdoor 
response measurements. 

accepted criterion for high-quality or "natural" reproduction such as 
is required for motion picture applications is flatness of response over 
the whole audible frequency range. This presumes, however, that 
the conception of flat response, or uniform pressure-frequency re- 
lationship is adequately understood. 

The so-called free-field pressure measurement is the only type in 



1948 



THEATER LOUDSPEAKER SYSTEM 



387 



which complete uniformity of pressure with frequency is at all likely 
to be found, and exact free-space conditions are very difficult to 
realize. Fig. 1 shows a satisfactory arrangement of horn and micro- 
phone for outdoor measurements. Furthermore, except in the ideal 
case where the pressure distribution is identical at all frequencies, 
uniform free-field response at a point does not indicate a uniform 
power-radiation condition, which is probably nearer to the desired 
characteristic when the loudspeaker is to be used in an enclosed 
space. Since practical low-frequency speakers now in use are all less 
directive at low frequencies, a flat free-field response which might be 
excellent for outdoor situations is not at all desirable for indoor use. 
Indoor measurements, on the other hand, are rather difficult to 





500 1000 

FREQUENCY IN CYCLES PER SECOND 



Fig. 2 Free-field response of loudspeaker phased for optimum 
performance as judged by listening tests. 

make. Rotating microphones, multiple microphones, and various 
other devices are resorted to, but all have their shortcomings. The 
use of rooms with staggered wall surfaces which tend to increase the 
number of reflections, but to reduce the severity of the interference 
effects appears to have some advantages. A rather ragged response 
curve is obtained in such a room, but the peaks and dips are so close 
together that a reasonable response trend may be inferred from the 
data. Unfortunately, however, such measurements are useful only 
for a rough evaluation, for the room in which the speaker is actually 
to be used probably will have different characteristics. A great deal 
can be learned about frequency balance from data of this type, but 
the limitations of the measurement must be understood. 
Ideally it would seem that a speaker should have a perfectly smooth 



388 



HOPKINS AND KEITH 



October 



free-field pressure response whether its trend be flat or otherwise. It 
is recognized, however, that reflections and standing waves in rooms 
cause raggedness in response that is far in excess of that exhibited in 
the free-field response of high-grade loudspeakers, and that in many 
cases the speaker having a smoother outdoor response does not appear 
superior when measured under indoor conditions. Under listening 
conditions where music or speech is involved, the transient nature of 
the reproduced material makes the audible effect of reflections and 
standing waves less evident than they are with the single frequencies 
used in measurements. Reflected sound, however, constitutes the 
greater part of the energy audible to the observer under indoor con- 
ditions, so that a certain amount of "raggedness" must be present in 













































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FREQUENCY IN CYCLES PER SECOND 



Fig. 3 Free-field response of loudspeaker of Fig. 2 phased for 
smoothest free-field response. 

what is heard. This is true, of course, whether the sound source is 
"live" or whether it is radiated from a loudspeaker. In many in- 
stances, where multiple- or dual-loudspeaker systems are used, free- 
field response dips caused by out-of-phase radiation from the various 
sources may be completely obscured under an indoor setup. It is 
the opinion of most experienced observers, however, that while the 
ear tolerates a certain degree of nonuniformity, a loudspeaker having 
a smooth response will generally be more acceptable under all listening 
conditions. 

In connection with the free-field dips in response which may result 
from the relative phasing of the sources in a multiple-unit speaker, 
Figs. 2 and 3 are of particular interest. The free-field response of a 



1948 



THEATER LOUDSPEAKER SYSTEM 



389 



loudspeaker system phased for optimum performance as judged by 
listening tests is shown on Fig. 2. The same speaker phased for the 
smoothest free-field response is shown on Fig. 3. 

In regard to the "flatness" of response and the frequency range, 
present-day high-quality speaker systems do not, in general, follow 
the pattern of idealized response. In practically all high-quality re- 
producing systems, the high-frequency response is purposely 
"drooped" to provide the most natural and pleasing quality from the 
listener's viewpoint. In many instances "tailoring" is provided to 
enhance "presence" or to compensate for some defect in the recording 
>r reproducing medium. It is interesting to note, that while the ear 




500 1000 

FREQUENCY IN CYCLES PER SECOND 



Fig. 4 Superposed response curves taken every 5 degrees off 
axis in horizontal direction. 

irs a certain tolerance for sharp variations in sound pressure, it is 
able to discern rather small changes in response trend. It has been 
demonstrated that a "hump" 1 decibel in magnitude at about 2000 
cycles tapering to zero at 1000 and 3000 cycles is easily detectable on 
an A-B test (direct comparison of "with" and "without" conditions). 
Many engineers are of the opinion that a "hump" in this frequency 
range is desirable for the enhancement of "presence." This leads to 
the conclusion that while measurement is an essential part of loud- 
speaker development, the ear, as the final judge, must be resorted to 
for the last adjustment to take care of subjective reactions under the 
actual conditions of use. 

On the other hand, the importance of the response curve to the de- 
lopment engineer must not be minimized. For example, let us 



390 



HOPKINS AND KEITH 



October 



consider Fig. 3 showing the outdoor axial response of the new Western 
Electric RA-450 60- watt system. The engineer, who is familiar with 
the acoustic environment of the setup used, will recognize this as one 
of the smoothest response characteristics that has been attained in 
the highest-quality loudspeaker systems. He will appreciate from 
experience that the relatively small irregularities which appear closer 
together with increasing frequencies are caused by reflections which 
he has been unable to avoid even in a very careful setup. The low-end 
response is found to be rising at a rate of approximately 6 decibels 
per octave which indicates a uniform radiation of power over this 
range. At higher frequencies, where uniform distribution is obtained 
the response is flat which indicates a uniform power radiation in this 



.EDGE DAMPING 



EDGE DAMPING - 




POLE PIECES 



MAGNETS 



VOICE COIL 



-ACOUSTIC RESISTANCE 

Fig. 5 Cross section of low-frequency unit. 



range. In measuring this response curve, the diaphragms of both 
low- and high-frequency units have been located so as to be the same 
distance from the measuring microphone, and, therefore, no irregular- 
ites around crossover are indicated. The engineer realizes, however, 
that he could have separated the diaphragms by a distance equal to a 
half wavelength at crossover frequency and obtain an outdoor curve 
indicating irregularities in response around crossover. He also recog- 
nizes that while the outdoor response of such a setup would look in- 
ferior, the speaker would sound just as satisfactory under listening 
conditions. His indoor response curves will not show these phasing 
difficulties due to crossover. 

DISTRIBUTION 

The most frequently published loudspeaker frequency-response 
curves are those measured on the axis of the speaker in free space. 
Such data are a measure of a very minute portion of the total energy 



1948 



THEATER LOUDSPEAKER SYSTEM 



391 



radiated by the device, and were nothing more known about the 
speaker, they would provide a very incomplete picture of the perform- 
ance of the instrument. For most applications it is conceded that 
the response of the speaker should be uniform over an angle encom- 
passing the area in which listening is to take place. For outdoor in- 
stallations this is usually a simple and logical requirement to set. 
When the device is intended for use indoors, however, the situation 
is not so clear-cut. No loudspeaker known at the present time will 
provide uniform response over a desired area and zero response out- 
side this area. Thus, in a room such as would be suitable for listening, 




500 1000 

FREQUENCY IN CYCLES PER SECOND 



Fig. 6 Impedance of low-frequency unit computed at high side 
of 24- to 4-ohm transformer. 

much of the sound reaching an observer's ears will be reflected energy, 
and the effect of the directional characteristics minimized. In spite of 
this situation, most experienced observers agree that a uniform direc- 
tional characteristic is a desirable attribute even for indoor listening. 

It is very difficult to design a practical loudspeaker which is capable 
of producing the same directivity pattern for all frequencies in its 
radiation spectrum. Multiple-unit devices approach this objective 
by limiting the frequency range reproduced by the individual units. 
As will be evident from an inspection of Fig. 4, two unit systems may 
be made to produce a remarkable uniformity of distribution. Wide 
variations of pressure are observed to occur at only one or two fre- 
quencies throughout the range at the extremes of the coverage angle. 

Sectoral horns, if carefully designed, are capable of producing uni- 
form radiation patterns over wide frequency ranges. The desirable 



392 



HOPKINS AND KEITH 



October 



directional characteristics are obtained at frequencies where the wave- 
length of the radiated sound is small compared to the width of the 
sector measured at the horn mouth. For this reason they are ex- 
cellent devices for use with high-frequency units. Because of the size 
involved, it becomes economically impracticable to use sectoral horns 
as low-frequency radiators. Flat-mouth, rectangular section, low- 
frequency horns are commonly used because of their structural sim- 
plicity, but they have the disadvantage that their directionality in- 
creases with frequency. This may be compensated by proportioning 
the mouth so that it provides the desired distribution of sound at the 



\ 




500 1000 

FREQUENCY IN CYCLES PER SECOND 



Fig. 7 Free-field response of low-frequency unit in box baffle. 

crossover frequency. If the low-frequency houdspeaker is then de- 
signed with a drooping low-end response under free-space conditions, 
the energy radiated may be made to be approximately uniform. 
Under indoor conditions, a satisfactorily uniform spread of energy 
will be apparent when these design objectives are attained. 

EFFICIENCY AND POWER CAPACITY 

The acoustic output available from a loudspeaker at which accept- 
able freedom from distortion exists and at which no mechanical failure 
occurs, is, in general, limited by the mechanical design. An increase in 
the efficiency of the device can only make it possible to achieve this 
limiting output with lower-powered amplifiers. A compromise be- 
tween the cost and weight of amplifier and loudspeaker must be 
struck in the interests of over-all system economy. Obviously effi- 
ciency, power capacity, and amplifier power must be considered in 
determining the needs of a given installation. 



1948 



THEATER LOUDSPEAKER SYSTEM 



393 



A method of determining the loudness-efficiency rating of loud- 
speakers, and of applying it to power requirements in enclosures has 
been described at a meeting of this Society, 1 and published in the 
Proceedings of the I.R.E. When measured in accordance with this 
method, a loudness efficiency rating of 20 per cent is indicated for the 
loudspeakers described herein. This efficiency is based on the acoustic 
power radiated over a 300- to 3000-cycle sweep-frequency band and is 



ENCLOSURE FOR TERMINALS 



DIAPHRAGM 



POLE PI EC 




MAGNET 



Fig. 8 Cross section of high-frequency unit. 



higher than the figure for previous commercial Western Electric 
systems. An accurate comparison with other systems is not possible 
until they are measured on the basis given in the above paper. 

While the efficiency of loudspeakers is generally regarded as an im- 
portant consideration in determining their suitability, it is a term 
which is frequently misinterpreted. Axial-response data are often 
exhibited as an indication of efficiency, whereas, as has been pointed 
out, this is a measure of a very small portion of the energy radiated. 
The directivity must be taken into account in any determination of 
efficiency based on pressure response. 

DAMPING 

Horn-type speakers, if used for the frequency range well above" the 
designed cutoff frequency of the horn, usually have well-damped 
mechanical systems. Because of size limitations, however, it is 



394 



HOPKINS AND KEITH 



October 



customary to use low-frequency horns at frequencies down to, and even 
below, cutoff. At these extremely low frequencies, the air loading will 
be small, and other means must be resorted to. Acoustical and 
mechanical resistance elements have been built into the Western 
Electric speakers to provide the required low-frequency damping. 
Such features result in a ' 'firmer," less boomy, bass response. The use 
of bass "booster" devices is, in general, inimical to well-damped 
response. 





Fig. 9 Sectoral high-frequency horn. 

DISTORTION 

The problem of distortion ratings for loudspeakers is rather com 
plex. Speakers do not, in general, exhibit uniform distortion-fre 
quency characteristics, and, therefore, the choice of frequencies o 
which to base distortion measurements is likely to be different fo 
each type of instrument. Furthermore, loudspeakers may produc 
relatively large amounts of distortion in one or two narrow-frequenc 
bands, and it is difficult to evaluate the subjective effect due to such 
condition- as compared to a smaller degree of distortion over a wide 
frequency range. It would seem reasonable to base a distortioi 
rating on total acoustic power output, which makes it necessary t 
search wide-frequency bands over wide-dispersion areas, or to comput 
the acoustic outputs at the various frequencies through the use o 



1948 THEATER LOUDSPEAKER SYSTEM 395 

a theoretically derived directivity index. The problem of distortion 
measurements in loudspeaker systems is not insoluble, but up to the 
present time only limited work in this field has been undertaken, and 
no standardized procedure has been worked out. It must be pointed 
out, too, that the results of steady-state measurements may not be a 
proper indication of the performance of a device intended to reproduce 
chiefly transient material. 

Certain facts are obvious, however, and qualitatively, at least, the 
distortion may be controlled. It is known, for instance, that non- 
linearity must exist in a system in order for distortion to be present. 
Consequently, control of stiffness and utilization of a linear flux field 
over the amplitude range required will control the first-order effects. 
Since various modes of diaphragm vibration may show up within the 
frequency range, and since nonlinearity may exist in some of these 
modes, distortion may result. Such modes, however, may be con- 
trolled by the judicious use of damping material. Listening tests 
usually will evaluate the efficacy of the measures taken. The effect 
of such damping on both the steady-state and transient response plays 
a large part in the clean performance of a high-quality loudspeaker 
system. 

DESIGN FEATURES OF NEW SYSTEMS 

With the above considerations in mind a series of theater loud- 
speakers has been designed to cover the range of power input and 
angular distribution needed for theaters of various sizes and shapes. 
In designing these horn systems, a crossover frequency of 800 cycles 
was chosen as the result of listening tests on systems having various 
crossover frequencies. It has been found an advantage to have any 
effects due to out-of-phase conditions between the low- and high- 
frequency loudspeakers come above the region of maximum energy 
transmission rather than in the middle of this range. This relatively 
high crossover frequency makes it possible to use smaller high-fre- 
quency units since less power is transmitted in the high-frequency 
horn system. It also makes possible the use of a smaller high-fre- 
quency horn due to its higher cutoff frequency. However, such a 
crossover is possible only through the use of a low-frequency unit and 
horn designed to transmit adequately the wider low-frequency band. 
A new type of low-frequency unit and a special low-frequency horn 
make this possible. 

The low-frequency units, Fig. 5, utilize a comparatively flat dia- 
phragm in place of the usual cone in order to reduce phase differences 



396 



HOPKINS AND KEITH 



October 



in the sound radiated from different portions of the diaphragm. The 
diaphragm surface is designed to provide high rigidity with light 
weight and to reduce "breakup" of the diaphragm at higher frequen- 
cies. This is accomplished by means of an approximately spherical 
central dome and an outer portion in the form of a surface of revolu- 
tion of a logarithmic curve. The voice coil is attached at the junction 
of the central dome and the curved outer surface. The arrangement 




Fig. 10 Front view of 60-watt theater system. 

of permanent magnets (Alnico 5) is shown in Fig. 5, consisting of two 
cylindrical magnets, one inside of the other. This provides high flux 
density with minimum weight and depth. Special acoustic and me- 
chanical resistance elements provide relatively high damping. This 
is illustrated by the impedance curve, Fig. 6. The unit has excellent 
high-frequency response as shown in Fig. 7 and is used in many in- 
stances as a full-range loudspeaker, but in this system it is utilized 
only for the range between 50 and 800 cycles. 

The low-frequency horn has an exponential taper with a sector- 
shaped horizontal section. This makes possible the combination of 



1948 THEATER LOUDSPEAKER SYSTEM 397 

two low-frequency horns side by side for additional power output 
without making the combination too directional. The low-frequency 
units are mounted in an enclosed cavity back of the horn which ob- 
viates the difficulties due to back radiation, such as an increase in 
response at certain frequencies and a decrease at others with attendant 
"hangover." Sound-absorbing material within the cavity prevents 




Fig. 11 Rear view of 60- watt theater system. 

standing waves, which might react on the diaphragm and cause ir- 
regularities of response. Flat baffle sections are provided to improve 
the response at low frequencies without producing resonant effects. 

The high-frequency units used in this system are similar to units 
previously used except for increased power capacity and efficiency. 
The former is accomplished by the use of a phenolic diaphragm and 
the latter by an improved permanent magnet. As shown in Fig. 8, 
sound waves created by motion of the diaphragm are conducted 
through expanding channels to a throat extending through the central 
pole. These units are capable of excellent reproduction up to con- 
siderably above 10,000 cycles. 



398 HOPKINS AND KEITH 

High-frequency horns are designed as single units with exponential 
taper and a horizontal section of uniformly increasing width. This 
sector-type construction is simple and capable of giving smoother re- 
sponse at high frequencies and better distribution than previous types. 
The design is such that two horns, designed for a horizontal distribu- 
tion of 50 degrees, Fig. 9, each with a driving unit, may be combined 
to give one horn of 100-degree distribution. This combination avoids 
the possibility of impedance irregularity which may occur when a 
double throat is used on a single horn. An 80-degree horn of similar 
design is used where this distribution angle is required. 

The dividing network is designed to operate from an amplifier 
having an output rating impedance of 24 ohms although both low- 
and high-frequency units have impedances of 4 ohms each. This re- 
duces the size of the network and the wires leading to it from the pro- 
jection booth. Step-down transformers are incorporated in both 
low- and high-frequency circuits to provide a proper impedance match 
whether one or two units are used in either low- or high-frequency 
circuits. An adjustable attenuator having 1-decibel steps between 
and 5 decibels is included in the high-frequency circuit. 

Outdoor measurements on a typical system (60-watt, 100-degree) 
are shown in Figs. 3 and 4. Fig. 3 shows response on the axis while 
Fig. 4 consists of superposed curves taken every 5 degrees off the axis 
in a horizontal direction. It will be noted that except in the neigh- 
borhood of the crossover frequency, 800 cycles, the curves for the 
various horizontal angles fall very close together. The departures 
near crossover are only at the extreme angles and cover such narrow- 
frequency bands that they can be neglected. The general construc- 
tion of a typical system is shown in Figs. 10 and 11. 

REFERENCE 

(1) H. F. Hopkins and N. R. Stryker, "A proposed loudness-efficiency rating 
for loudspeakers and the determination of system power requirements for en 
closures," presented April 24, 1947, at the SMPE Convention in Chicago; Proa 
I.R.E., vol. 36, pp. 307-315; March, 1948. 



Modern Film 

Re- Recording Equipment* 

BY WESLEY C. MILLER 

METRO-GOLDWYN-MAYER STUDIOS, CULVER ClTY, CALIFORNIA 
AND 

G. R. CRANE 

WESTERN ELECTRIC COMPANY, HOLLYWOOD, CALIFORNIA 

Summary Here is described a recently installed modern cabinet-type re- 
recording equipment, having a completely new approach in design and opera- 
tion. Radically new, but proved features have been incorporated for ease 
and economy in installation, operation, and maintenance. The over-all 
functional design is based on original concepts by Metro-Goldwyn-Mayer 
and includes the manufacturer's recent basic developments in film-pulling 
mechanisms and optical systems. 

THE RECENT completion of the new film re-recording installation 
at the MGM Studio in Culver City and the progress of the 
parallel installations in the Elstree -Studio in London and the various 
MGM International Studios suggest it may be an opportune time 
to describe the installation and apparatus components and to com- 
ment on the underlying philosophy of the design concepts involved. 

Some preliminary work was done several years ago resulting in the 
completion of experimental models of apparatus units described at 
that time 1 . As a result of the experience gained from operation with 
these models, and also to take advantage of the improved film 
motion developed by Western Electric, for which recognition was 
recently given by the Academy of Motion Picture Arts and Sciences, 
further design work has resulted in the present MGM units. This 
paper primarily will be concerned with the re-recording machine, and 
although a number of special features were custombuilt for the MGM 
installations, the basic design principles are incorporated in the 
standard Western Electric units. 

Motion picture re-recording has many ramifications. It is a part 
of the picture-making technique which reflects the sound engineer's 
ingenuity in finding answers to the many problems, suggestions, and 

* Presented May 17, 1948, at the SMPE Convention in Santa Monica. 

OCTOBEK, 1948 JOURNAL OF THE SMPE VOLUME 51 399 



400 MILLER AND CRANE October 

inspirations presented by all of the other individuals and groups who 
contribute to the finished product. It is also the place where the 
soundman ceases to be an engineer and becomes a controlling and 
creative factor hi the successful presentation of the product to the 
public. To an increasing degree the interpretations of the producer, 
the director, the musician, and the editor are dependent upon the re- 
recording processes and upon the skill and understanding of the re- 
recording mixer. 

There was a time when a single domestic release negative would be 
re-recorded from perhaps three or four sound tracks, made up of a 
dialog track, .one or two music tracks, and one or two effects tracks. 
Such simplicity sometimes would be welcome now but the require- 
ments and demands of the modern product require a great deal more 
complexity. Eight re-recording tracks are probably a fair average 
requirement and the need to use ten or twelve tracks arises fre- 
quently. In particularly complicated reels or sequences there are 
many cases where twice this number of tracks may be used. 

It is common practice to make sound effects and music negatives 
for foreign synchronized versions at the same time that the domestic 
release version is re-recorded. This involves additional recording 
machines together with the amplifier channel extensions needed for 
the multiple job. Moreover, a 16-mm version is now standard 
practice. Added to these requirements is the need for several 
productions to be in work at the same time, together with all of the 
routine preparation of playback material for production stage use, 
temporary re-recording for immediate editorial purposes, publicity 
and broadcast material, and other irregular but continuing demands. 
This variety of requirements obviously presumes a large amount of 
equipment. For the MGM Culver City Studio this necessitates forty- 
one film reproducers, or film dummies as they are commonly known, 
and eight film recorders, of which some are for theater release 100-mil 
variable-density track, others for 200-mil push-pull for various studio 
and international uses, one is for 16-mm release and another for vari- 
able-area release when required. These machines operate with any 
one of four re-recording channels and from corresponding re-recording 
auditoriums and projection rooms. To these film facilities is added 
the necessary disk equipment for recording and reproducing which 
are constantly in demand. Later there will be magnetic equipment 
as well. 

The artistic phase of re-recording and the technique of equalization, 



1948 FILM RE-RECORDING EQUIPMENT 401 

balance, and editorial construction are of such nature that it may well 
be expected that they will be changing continually to conform to 
current and future requirements. While there are certain elements 
of uniformity, departures from the uniform pattern are not only ex- 
pected but are to be desired in the attempt to produce improved 
entertainment and technical quality. 

On the other hand, the physical handling of film material from 
which re-recording is done is a matter which should be undertaken on 
a basis which is largely routine and which can be semiautomatic in 
character. It is with this phase of the work that the present dis- 
cussion is principally involved. 

EQUIPMENT REQUIREMENTS 

Some of the more important attributes of re-recording equipment 
which will meet present requirements and which may be expected to 
continue to meet these requirements for many years to come may 
readily be listed as follows: 

(1) Virtually absolute uniformity of film motion, regardless of 
film or drive irregularities. 

(2) Consistent and dependable operation of all electrical and op- 
tical elements. 

(3) Simplicity and rapidity of operation and manipulation. . 

(4) Ease and economy of maintenance. 

(5) Installation simplicity and economy. 

The experience of the past few months with the installation at 
Culver City has shown that the design concept is admirably suited to 
the operating requirements. Similar reports have been received from 
the smaller installations. 

MGM INSTALLATION 

Three kinds of equipment units are involved; a film recorder, 
its associated control cabinet, and the film reproducers, or re-record- 
ers. Fig. 1 shows the form which the equipment takes. Each unit 
is housed in a rectangular sheet-metal cabinet containing all of the 
equipment associated with the unit . The height and depth of all units 
are the same, with the width varying with the nature of the unit. 
This permits arranging the units in rows of any desired length and 
in any pattern which floor plan and operational procedure suggest. 

Inasmuch as all of the elements associated with a given unit are in 



402 



MlLLEK AND CRANE 



October 



the same cabinet, the complete unit can be completely assembled, 
wired, and tested under shop manufacturing conditions. The in- 
stallation thus becomes very simple as it requires a minimum of 
external wiring to terminal blocks in each cabinet. 

Past experience has shown that the installation costs are very high 
when it is necessary to install and wire a number of individual 




. 




Fig. 1 Typical arrangement of control cabinet, re- 
corder, and re-recorders as used at MGM Studio, showing 
similarity of the units. 

mechanical units, amplifiers, and all of the associated items when the 
work has to be' done as a matter of individual installation. As com- 
pared with this the installation of complete equipment units can be 
done quickly and inexpensively. 

In this connection, as will be shown in more detail later, one differ- 
ence between the MGM re-recorders and the standard Western 
Electric units lies in the arrangement of the panel above the film 



1948 



FILM RE-RECORDING EQUIPMENT 



403 



compartment of the re-recorder. An MGM requirement was the use of 
a six-position rotary switch in this location, arranged to switch the re- 
recorder interlock motor to any one of six separate distributor trunks. 
With a suitable safety provision in this switch it then becomes prac- 
ticable to shift a reproducer rapidly from use with one re-recording 
system to any other. This facility of interchange is important in 
saving time as assignments in various rooms are constantly changing. 
To accommodate these switches some fifty-odd trunk lines of power 
capacity are involved and with normal cabling and connection 







Fig. 2 Top view of equipment shown in Fig. 1, with covers removed to show 
the distribution of wiring and switching arrangement used at MGM. 

methods this would have been an expensive installation item. Fig. 2 
shows the solution attained. A flat bakelite-supported form was 
constructed before installation. At each junction point in the trunks 
and also at each switch connection appropriate Stakon connections 
were employed. When the equipment units were in place, the pre- 
fabricated flat form was dropped in place and the Stakon connectors 
plugged together. For a row of six reproducers and their associated 
recorder and controls the number of connections is of the order of 1200 
so that this substitution of Stakons and the prefabricated form for 
soldered connections and standard cable forms results in an appre- 
ciable saving in initial installation. The standard Western Electric 
machine uses this space for drawer-type mounting of the phototube 



404 MILLER AND CRANE October 

amplifier available from the rear, and the front area is used for lamp 
and other controls. In the MGM form the phototube amplifier is 
placed in the bottom compartment, also accessible from the rear. 

The floor plan for the MGM installation is shown by Fig. 3. In 
this case, each row of units includes six film reproducers, one film 
recorder, and one control cabinet, so that in the two opposing rows 
there is the direct association of twice this number of units. This 
choice of numbers and arrangement is based upon the particular 
experience and requirements at MGM. It varies, of course, among 
studios, and the use of existing building space is an important con- 
sideration. In the case of the MGM installation all of the units are 
finished in white enamel to accentuate the impression of cleanliness. 
This feature has created favorable comment and is of course a depar- 
ture from what has heretofore been thought of as standard practice 
for this type of equipment. 

The conventional overhead sprinkler system is used for fire pro- 
tection. However, high-temperature heads are installed to mini- 
mize the possibility of sprinkler operation at the wrong time. In 
this connection it should be noted that there is no potential fire- 
producing element in the machines themselves, barring the remote 
possibility of a static condition. 

RE-RECORDING MACHINE 

The film motion and mechanical drive are identical in the repro- 
ducer and recorder. Minor changes provide for the use of 17.5- 
mm film in the reproducer and of 35-mm film in the recorder. Aside 
from this there are, of course, the expected differences which permit 
the use of the proper modulator and of unexposed film in the recorder, 
whereas the reproducer is adapted for positive track and for the re- 
producing optical and phototube systems. A pair of the standard re- 
recorders is shown by Fig. 4 and the most unique features are perhaps 
the disappearing doors, the removable mechanism unit, the film path, 
and the optical system. A two-section cabinet permits the choice 
of a separate base cabinet unit, which may be either a plain unit or one 
containing a series of fixed and adjustable rollers for handling a loop 
up to 25 feet long. However, the loop may extend from one lower 
loop rack area into adjacent machines if desired. The cabinet itself 
is of rigid construction, well ribbed to avoid panel vibration, and has 
removable rear doors for accessibility to all components. 

In spite of the fact that the room in which this equipment is 



1948 



FILM RE-RECOKDING EQUIPMENT 



405 



d t 



d t 



I 



m 



I 



I 






406 



MILLER AND CRANE 



October 



installed may be air-conditioned it was deemed desirable to have doors 
which close the film compartments of the reproducers. The doors are 
of heavy glass and are so hinged that they are flush with the front of 
the cabinet in both the open and closed positions. When swung open 
they disappear into the sides of the cabinet. These doors normally 



*%!&*' 




Fig. 4 Two RA-1251-type re-recording ma- 
chines with the standard control panel and loop- 
rack cabinets. Left machine threaded for normal 
operation; right machine for loop operation using 
upper or lower racks or both. 

are operated manually .with rubber bumpers provided for protection, 
but in the case of the MGM machines, they are electrically operated 
by a momentary contact push button located at a convenient height 
on the side of the machine as shown in Fig. 1. Suitable precautions 
have, of course, been taken so that the hand or any obstacle caught in 



1948 



FILM RE-RECORDING EQUIPMENT 



407 



the door will cause the door to stall without damage or excessive force. 
These cabinets are intended to be anchored to the floor with wiring 
coming up through the floor. 

MECHANICAL DESIGN 

Attention is particularly invited to the unusual arrangement where- 
by the actual film-motion unit and its associated accessories for both 
reproducer and recorder are readily removable from the cabinet. The 
film-motion unit slides in and out from the rear and is arranged to be 
kept in mechanical alignment when it is pushed into place, and to 



V 



lls 




Fig. 5 Rear view of removable mechanism unit of the 
RA-1251-type re-recording machine. 

make the necessary electrical connections, with the exception of a 
plug to the phototube amplifier. In addition, each of the major 
mechanism components is removable as a complete subassembly and 
all such assemblies are interchangeable in case of emergency. This 
complete mechanism unit is shown by Fig. 5, and facilities are pro- 
vided for the removal and replacement of the various major subas- 
semblies without loss of precison adjustments. For example, the motor 
position is adjustable vertically and laterally for shaft alignment, 
after which the adjustments are locked and the motor and its base 
may be removed thereafter and replaced without losing the align- 
ment. The same principle is applied to the flywheel and drum 



408 MILLER AND CRANE October 

assembly to retain optical adjustments related to the portion of the 
optical system which is mounted within the scanning drum. 

The scanner assembly, shown by Fig. 6, contains a scanning drum 
driven by the film, and it is rigidly connected to a solid flywheel, the 
shaft being supported on two very small ball bearings so that the 
friction is held to a minimum and in addition, any moderate imper- 
fections in the bearings are negligible, thereby avoiding a high degree 
of bearing selection. Fig. 7 shows the gear-drive assembly which also 
contains the sprockets and associated pad rollers. The gear re- 




Fig. 6 Complete scanning drum and flywheel assem- 
bly, including optical subassembly under cap at end of 
scanning drum. 

duction is accomplished in two stages with the rear section contain- 
ing a high-ratio, right-angle drive for which gears are available to 
accommodate motor speeds of 720, 1000, or 1200 revolutions per 
minute, or other ratios as might be required for 16-mm operation. 
This assembly also contains a built-in clutch to disconnect the motor 
from the recorder mechanism so that the latter alone may be turned 
over by hand. It has been found to be a great convenience to be able 
to thread rapidly and then register the start mark on the film without 
disturbing the motor from its interlock position. The clutch is, of 
course, of the positive type which does not permit any slip during 
normal operation. The sprockets have flanges to facilitate threading 



1948 FILM RE-RECORDING EQUIPMENT 409 

and improve film guiding. The sprocket teeth are unusually large, 
having a base of 74 mils in the direction of the film. With a base diam- 
eter of 0.942 inch, this sprocket permits nearly optimum operation 
over a shrinkage range of to 0.8 per cent and considerably greater 
shrinkage can be accommodated without significant damage to the 
film. These sprockets reduce to negligible amount the so-called 
"crossover" effect, which is the erratic motion of the film over the 
sprocket within the limit of sprocket-tooth clearance in the sprocket 
holes. The sprocket pad rollers are of uniquefdesign in which the pad- 



Fig. 7 Complete drive-unit assembly from motor coupling 
to sprockets. Vertical lever releases built-in clutch for thread- 
ing release. 

roller assembly pivots in the same plane as the sprocket axis and the 
finger pads are lo'cated so that the two pad-roller assemblies may be 
opened simultaneously by the thumb and first finger. Fig. 8 shows 
the filter-arm subassembly consisting of two rollers mounted on 
pivoted arms controlled by springs and arranged so that only the 
rollers appear through slots on the front of the panel. One spring pro- 
vides for the tension in the film path between two sprockets. The 
other spring compensates for the total accumulated friction of all 
rotating components in the path between the two sprockets. This is 
sometimes referred to as the "gravity spring" and is anchored to the 



410 



MILLER AND CRANE 



Octobei 



frame through a cam control appearing on the front of the panel) 
This cam then becomes a vernier adjustment of synchronization whilj 
the machine is running or stationary, and a range of approximately i 
2 sprocket holes is available. The filter rollers as well as. the fixed 

rollers in the film path are, ol 
course, ball bearing with pre ]; 
cautions taken to reduce friction] 
to a low value. The lower arni 
is provided with a fluid dashpolj 
for proper damping and is arl 
ranged to prevent spillage of thl 
fluid at any angle. 

Film rewinding is provided bjl 
a motor and gear-reduction unit 
located behind the upper pane 
and connected to the feed-reel 

4 |1 shaft with an automatic cuton 

assembty located in the uppei 
right-hand corner of the angle 
plate assembly. This facility 
provides automatic rewind once 
the film is threaded and rewind 
ing started by the operator throw' 
ing a small idler roller into con 
tact with the film. The rewinc 
time is adjustable between 3( 
seconds and one minute for 10CK 
feet of 35-mm film and the film 
velocity is reasonably constanl 
as provided by the usual char- 
acteristics of a high-speed, series-type motor. 

FILM MOTION 

The film propulsion of this machine is essentially the same in prin- 
ciple as that previously described in the JOURNAL. 2 As shown by Fig. 
9, a taut film path between two 16-tooth sprockets drives a scanning 
drum and flywheel by belt action, and passes over two compliance) 
rollers, one to the left of each sprocket. One of these rollers id 
provided with viscous damping and this film-propulsion system hasj 
demonstrated its ability to suppress all mechanical disturbances genern 
ated in the drive mechanism as well as those caused by film splices. 







Fig. 8 Filter-roller assembly show- 
ing damping device attached to lower 
roller arm and locking lever which is 
actuated by the lower sprocket pad 
roller. Spring at right determines 
film tension in filtered path and that 
at left is anchored on cam for syn- 
chronization adjustment. 



1948 



FILM RE-RECORDING EQUIPMENT 



411 



As an aid in threading, the two filter rollers are locked in the normal 
operating position when the lower sprocket pad roller is open for 
threading. Threading is therefore reduced to a very simple and fast 
Dperation since no loops are required. As the film is placed over the 
lower sprocket and the pad roller closed, the filter arms are thereby 




Fig. 9 Front view of mechanism unit showing film threaded 
for operation. 

released and ready for operation. As previously described, the clutch 
button may then be used for setting the start mark. 

OPTICAL SYSTEM 

The optical system employed in this re-recorder is somewhat of a 
departure from previous optical systems and was designed to meet the 
requirements of convenience in operation, relatively high efficiency, 



412 



MILLER AND CRANE 



Octoben 



freedom from fire hazards, and versatility in scanning any type oij 
track in current use, with a high degree of uniformity in light in-j 
tensity and definition in the scanning beam. Years of practical 
experience in optical systems have demonstrated the safety of son 
called front-scanning systems, but these systems are not readily obJj 
served for scanning performance and require frequent use of various^ j 
types of alignment or test tracks. The convenience of rear-scanning 
systems for visually determining scanning is well known, but manw 



PHOTOTUBE 




CYLINDRICAL LENS 
SPHERICAL LENS 

SPHERICAL LENS 
SPHERICAL LENS 
CYLINDRICAL LENS 

CYLINDRICAL OBJECTIVE LENS 
YLINDRICAL OBJECTIVE APERTURE MASK 

CYLINDRICAL RELAY LENSES 
-SLIT MASK 

"CYLINDRICAL CONDENSER LENS (VERTICAL) 
"CYLINDRICAL CONDENSER LENS (LATERAL) 

"CURVED FILAMENT EXCITER LAMP 



Fig. 10 Optical schematic, with omission of prism and mirrors used only for I 
turning optical axis by 40 degrees. 

such systems have contained fire hazards because of the relatively]' 
large amount of light placed upon the film by the condenser-lens i 
system. In order to retain the advantages of each of these systems, II 
the one used in this machine combines the convenience of rear scanning| 
with the safety of front scanning. This is accomplished by using 
the front-scanning method of placing a scanning line upon the film in] 
which the width of the line determines the frequency characteristic! 
in reproduction, but which is of sufficient length to more than cover I; 
the area occupied by all sound tracks in current use. A rear-scanning i 
type of system is employed whereby an enlarged image of the film and] 



1948 FILM RE-RECORDING EQUIPMENT 413 

this scanning line is produced upon a mask so that the limits of scan- 
ning are readily observable and adjustable at any time. Fig. 10 shows 
this system schematically, omitting a prism and mirrors which merely 
turn the optical axis by 90 degrees for mechanical convenience. 

The basic requirement of the front-scanning section was that of pro- 
ducing a line in which the intensity and the definition were to be reason- 
ably uniform throughout its length as well as being highly efficient. 
This was accomplished by the use of cylindrical lenses only and the 
scanning line is an image of a physical slit produced by a relatively 
short focal-length cylinder. The height of this line is equivalent to an 
ideal scanning slit of approximately 1.0 mil and its quality and defini- 
tion are quite uniform throughout its length. The illumination is 
uniform to within 0.5 decibel. The light source is a 10-volt, 5- 
ampere, curved-filament lamp and the optical constants are such that 
its vertical position is not critical, thereby permitting prefocused 
lamps and essentially eliminating microphonic noise generated by 
lamp vibration. The stereopticon type of system is used and the 
advantages of the curved-filament lamp have been described by 
Carlson. 3 

The rear-scanning system consists of a combination of spherical 
and cylindrical elements, the design of which is primarily dependent 
upon the ability to collect and control all of the light coming from the 
scanning assembly and to meet the physical requirements of the 
machine design. It consists of three spherical lenses with the ad- 
dition of two cylindrical elements between the film and the scanning 
mask. The first cylinder is located just behind the film to collect the 
relatively large vertical angle of light, and this cylinder in com- 
bination with a negative cylinder located on the rear of the third 
spherical lens produce a vertical enlargement of the scanning line of 
the order of 100 : 1 to permit more convenient observation of the 
scanning limits relative to the mask. Although not shown on Fig. 9, 
there is a prism located between the first two spherical lenses for the 
purpose of offsetting the beam to clear the scanning drum. Other 
mirrors are used to bend the light depending upon the particular 
application. The three spherical lenses produce an image at the mask 
which is magnified laterally approximately 3 : 1 and a scanning mask 
contains three sets of openings, one of which is registered with the 
projected light beam to limit the scanning. These openings provide 
for 200-mil push-pull in either the standard or offset positions and 
for 100-mil single or push-pull. In the vertical direction all of the 



414 MILLER AND CRANE October 

projected light beam being scanned passes through the opening in the 
mask and appropriate field lenses are located just behind these open- 
ings to direct the light into the phototube. An RCA 920 tube is used 
and the patterns on the cell cathodes represent filament images about 
I /B by 3 /s inch long so that they are readily accommodated by the 
standard cathode construction. These images are essentially variable 
in intensity only, regardless of the manner in which the light is atten- 
uated at the film plane. Fig. 11 shows the mechanical embodiment 
of the optical assembly between the lamp and the film. In this 




Fig. 11 Complete scanning optical system from 
lamp to film, which places the lamp behind the 
front panel and produces a line of light on the film 
1 mil high by 230 mils long. 

machine the lamp is located behind the front plate to eliminate all 
heat and fire hazard. A mirror turns the axis 90 degrees and this 
complete subassembly contains lateral and vertical lamp adjustments 
as well as focus and azimuth adjustments. The latter is attained by 
a rotation of the entire subassembly about its optical axis. The 
scanning assembly contains the third spherical lens of the collector 
system, the scanning masks, field lenses, and associated controls. 
The left-hand knob controls the position of the mask for the type of 
scanning desired. The right-hand knob moves the mask laterally for 
proper scanning registration and this knob is calibrated to indicate 
the normal scanning position or the departure from this normal with 



1948 



FILM RE-RECORDING EQUIPMENT 



415 



calibration in mils. A viewing window is provided on the front of 
this assembly with a sliding cover. This system has met the design 
objectives and gives an output signal at the phototube which results 
in an unusually high signal-to-noise ratio relative to mechanical 
disturbances which frequently have been so troublesome in the past. 
This optical system has also been applied to theater-type sound- 
heads and a typical example is shown by Fig. 12. The same facilities 




Fig. 12 Theater- type reproducer using the same optical system as Fig. 10. 

are available and the performance is essentially equivalent. In this 
case the elements between lamp and film are contained in a circular 
tube, and are designed to conform to the usual distance between lamp 
and film, which is approximately 4 7 /i 6 inches. 

PHOTOTUBE AMPLIFIER 

The phototube amplifier employes a new feature heretofore not 
used on this type of equipment. This consists of a special feedback 
input circuit which permits several feet of shielded cable to be used 
between the phototube mesh and the amplifier. By locating the 



416 



MILLER AND CRANE 



October 



amplifier away from the congested area around the machinery, greater 
freedom of design is obtained both for the mechanical system and for 
the amplifier. Also less microphonic noise and other noise disturbance 
generally will be obtained with the separation. Ordinarily the capac- 
itance associated with a cable connecting phototubes and amplifier 





Fig. 13 Phototube coupling unit showing front view with phototube 
switch and balancing controls, and rear view with cover removed. 

would cause a serious loss of high-frequency response. However, in 
this application the feedback from plate to grid of the first tube 
effectively cancels the capacitance of the cable so that an approximately 
flat frequency characteristic is obtained up to about 8000 cycles per 
second. No appreciable loss in signal-to-noise ratio is incurred over 
that of more conventional methods. The amplifier has three 
stages with feedback around the last two stages as well as the* first 
stage. In the standard machine, it is mounted on a drawer 



1948 FILM RE-RECORDING EQUIPMENT 417 

arrangement which plugs in, thus providing for good accessibility 
and quick change in case of emergency. 

Fig. 13 shows the phototube-coupling unit consisting of a complete 
assembly mounted on rubber. It contains all of the electronic com- 
ponents necessary for coupling the phototube through a single un- 
balanced, shielded line to the amplifier which is several feet away. A 
push-pull to parallel switch and a balancing potentiometer for push- 
pull balance adjustment are available through the front of the panel, 
but normally are under a cover since they are merely routine main- 
tenance adjustments and are not required during operation. 

CONCLUSION 

At present the re-recording operations throughout the industry are 
almost entirely from film reproduction to film recording. However, 
there are good prospects of the adoption of magnetic methods for all 
original studio recording and for all editorial work. The adaptation 
of this new equipment to magnetic methods w~as kept in mind during 
its design so that the change can be made with a moderate amount of 
difficulty and expense. It is anticipated that magnetic methods will 
be useful for every phase of studio work up to, but excluding, the 
actual release negative. 

The experience thus far with this new equipment at MGM and 
elsewhere has been remarkably good. Uniformity of operation from 
machine to machine had heretofore been difficult to attain with a 
large number of machines. At MGM the machines are now assigned 
to any class of work by number and any departure from uniformity 
is virtually unheard of. The arrangement of machines and the 
rapidity of threading and rewinding have greatly reduced the time 
between successive rehearsals and takes. This is of importance to 
the mixers and the producing group since it increases the amount of 
production material which can be completed in each room each day 
and thereby reflects directly on the operating economy of the re- 
recording work. 

REFERENCES 

(1) Wesley C. Miller, "The MGM recorder and reproducer units," J. Soc. Mot. 
Pict. Eng., vol. 40, pp. 301-326; May, 1943. 

(2) C. C. Davis, "An improved film drive filter mechanism," /. Soc. Mot. Pict. 
Eng., vol. 46, pp. 454-464; June, 1946. 

(3) F. E. Carlson, "Properties of lamps and optical systems for sound reproduc- 
tion," J. Soc. Mot. Pict. Eng., vol. 33, pp. 80-97; July, 1939. 



Motion Picture Research Council* 

BY W. F. KELLEY 

SECRETARY-TREASURER, MOTION PICTURE RESEARCH COUNCIL, 
HOLLYWOOD, CALIFORNIA 



Summary The purpose of this paper is to explain the organization, func- 
tions, and activities of the Motion Picture Research Council, Inc.. A brief 
resume of the Council's history and the reasons for its reorganization will be 
given as an introduction. 

SHORTLY AFTER the organization of the Academy of Motion Pictim 
Arts and Sciences in 1927, a technical bureau was formed withinl 
the Academy. The technical bureau, under the chairmanship 01 
Irving Thalberg, collected and published information on the use 01 
incandescent lamps on sound sets, conducted courses in industrial 
education, and contributed materially to the solution of many prob^ 
lems encountered in establishing sound in motion pictures. 

In 1932, the Academy was reorganized. The Research Council reJ 
placed the technical bureau and functioned under the Academy by- 
laws, but was sponsored and financed by the Association of Motion 
Picture Producers. The governing body of the Research Council 
consisted of one technical representative from each of the ten studios, 
plus an executive-producer chairman. These chairmen have been 
S. J. Briskin, William Koenig, Darryl Zanuck, and Y. Frank Freeman. 

Experience in the operation of the Academy Research Council 
demonstrated the restrictions of its particular organizational struc- 
ture. Its activities were limited by lack of funds and staff, and the 
necessity of operating through committees of technicians volunteering 
their tune. However, the work of the Academy Research Council 
demonstrated unmistakably the need and the possibilities of a prop- 
erly organized and adequately financed research and development 
program. 

Several proposals for a research program were presented to and 
discussed by studio executives, both in Hollywood and in New York. 

* Presented May 17, 1948, at the SMPE Convention in Santa Monica. 
418 OCTOBER, 1948 JOURNAL OF THE SMPE VOLUME 51 



RESEARCH COUNCIL 419 

A committee of Herbert Freston, Peter Rathvon, and Y. Frank Free- 
man, was appointed to decide upon a plan for the producers. Two 
recommendations were made and approved. First, it was decided to 
appropriate sufficient funds to establish an expanded program with 
proper organization and adequate staff. Second, it was decided to 
use the existing Research Council as the nucleus of the new 
organization. 

As a first step, it was necessary to secure a director for the new pro- 
gram. In August, 1947, the services of Wallace V. Wolfe were ob- 
tained. His executive ability, engineering background, and broad 
knowledge of the motion picture picture industry made him particu- 
larly well qualified for this position. 

The second step was the establishment of a proper organization. 
Operation of the Academy Research Council under the Academy had 
been entirely satisfactory and practical, but limited. The new 
organization needed greater freedom of action. It had to be able to 
negotiate contracts, obtain patents, grant licenses, buy and sell prop- 
erty. It had to be responsible directly to its sponsors for the ex- 
penditure of funds. 

This was discussed with the Academy and the necessity for a change 
in the organization of the Council was recognized and approved by 
Jean Hersholt, president of the Academy, and the Academy Board of 
Governors. As a result, Herbert Freston drew up articles for a new 
corporation and the Motion Picture Research Council was estab- 
lished as a nonprofit California corporation on October 14, 1947. 
Under its bylaws, its purposes are to engage in engineering develop- 
ment and research, to find solutions to common problems, to develop 
and improve equipment and methods, to promote standardization 
and the interchange of ideas and information, and to act as a liaison 
between studios and suppliers. 

The corporation has ten company members : Columbia, Goldwyn, 
Loew's, Paramount, RKO, Republic, Roach, Twentieth Century- 
Fox, Universal, and Warner Brothers. These company members elect 
a board of twelve directors. As presently constituted, the board con- 
sists of one representative from each member company, plus an execu- 
tive-producer chairman and the president of the corporation. 

The management of the corporation is vested in a board of 
directors, the officers, and committees. 



420 KELLEY October 

OFFICERS 

WALLACE V. WOLFE, President R. A. KLUNE, V ice-President 

W. F. KELLEY, Secretary-Treasurer 

BOARD OF DIRECTORS 

Y. FRANK FREEMAN, Chairman 
THOMAS MOULTON, Vice-Chairman 

JOHN AALBERG GERALD F. RACKETT 

DANIEL J. BLOOMBERG ELMER R. RAGUSE 

FARCIOT EDOUART GORDON SAWYER 

BERNARD HERZBRUN DOUGLAS SHEARER 

NATHAN LEVINSON WALLACE V. WOLFE 

Committees are of three types: permanent committees, special 
committees, and task groups or subcommittees. Permanent com- 
mittees, appointed by the board, represent each major technical 
division of motion picture production. There are fifteen such per- 
manent committees: 

Art Direction Electrical Set Grip Equipment 

Color Laboratory Sound 

Directors of Cinematography Photographic Standards 

Editorial Production Managers Subgauge Film 

Effects Set Construction Television 

These committees are charged with the responsibility of acting in a 
technological advisory capacity to the board and staff on all activities 
pertaining to that committee's particular phase of production. 

Special committees, also appointed by the board, advise on par- 
ticular projects not within the scope of any permanent committee. 

Task groups, subcommittees of permanent committees, are ap- 
pointed to act in an advisory capacity on a single phase of a project, 
and to make recommendations directly to its permanent committee. 

The next step in the program was to secure proper quarters and 
staff personnel. Office and laboratory space was obtained at 1421 
North Western Avenue in Hollywood. This location has the ad* 
vantage of being adjacent to studio facilities where operating tests 
can be made. 

Personnel requirements were based on the recognition that produc- 
tion problems embrace every phase of the engineering profession. We, 
therefore, employed an engineer for each of the major phases of our 
program, consistent with the budget limitations of a new organization. 
At present, in addition to Mr. Wolfe and myself, we have on the staff 



1948 RESEARCH COUNCIL 421 

eight engineers with practical experience in chemistry, physics, con- 
struction, standards, electricity, lighting, and mechanical design. 

As the organization was being set up, specific activities were being 
outlined. Our program is still in its formative stage, but our present 
activities indicate our future program. 

First, the staff is analyzing new ideas and new inventions submitted 
for possible application to motion pictures. Since the first of the year 
we have considered such items as three-dimensional systems, tele- 
vision patents, special cameras, color systems, aerial and underwater 
photography, and universal focus lenses. 

Second, we are searching for and examining equipment and ma- 
terials developed by other industries for adaptation to the motion 
picture industry. Included are such items as magnetic recording, 
"liquid-envelope" materials, static eliminators, wall coverings, shellac 
substitutes, nylon products, and molded screens. 

Third, we are disseminating information to our member companies 
through reports and bulletins and by discussion in committee meet- 
ings. 

Fourth, we are promoting standardization through the establish- 
ment of industry practices and with a recommendation for American 
Standards where these industry practices apply. We are presently 
concerned with the standardization of screen illumination, dimen- 
sions and speed of magnetic-recording mediums, pitch of sound-re- 
cording negative, laboratory procedures for 16-mm release of 35-mm 
material, elimination of frame lines, Dubray-Howell perforation, and 
fused plugs and cables. 

Fifth, we are actively engaged in short- and long-range projects. 
Short-range projects may cover a period of a few days to a year or two, 
while long-range projects may cover from one to five years. We are 
now carrying on two long-range projects: set construction and set 
lighting. 

The purpose of the set-lighting project is to provide improved 
lighting methods and tools to enable production crews to accomplish 
their job with greater flexibility and improved efficiency. 

A review of the literature is in progress and a survey of present 
methods and techniques has been undertaken. This survey, partially 
completed, includes light sources, lamphouses, optical systems, 
filters, control equipment, power supply and, most important, the 
manner in which such equipment is used on the set. At the same 
time, an investigation was initiated to determine the possibility of 



422 KELLEY October 

employing new light sources which might be available. We are 
actively following the development of the mercury-cadmium compact 
light source and the zirconium lamp, and we are presenting designers 
and manufacturers with broad operating specifications for the motion 
picture use of. these lamps. Since this project is still in the staff-in- 
vestigation phase, results cannot be reported at this time. 

The set-construction project is also in the survey stage. A survey 
of present methods and the literature is being carried on simultane- 
ously with an investigation of the possibility of adapting products of 
other industries to the construction of motion picture sets. 

We have a number of short-term projects and it will suffice to ex- 
plain one of these in some detail and merely list the others. 

One of our short-term projects is the design and construction of a 
small camera crane. There has beeri greater and greater need for 
camera flexibility as production methods have progressed. The 
camera has advanced from the stationary tripod to the dolly and to 
cranes or booms. The dolly is somewhat limited in its use and the 
large crane unwieldy and expensive to operate. Therefore, there is a 
need for a crane with the mobility and flexibility of a dolly, but with 
the camera range and broader application of the large crane. Several 
small cranes had been developed previously. Metro-Goldwyn-Mayer 
built, and still has in use, several cranes of intermediate size. Sub- 
sequently, Twentieth Century-Fox developed a small, motor-driven 
crane. The Council's crane is similar, differing mainly in the type of 
construction and accessories. 

Acting under the direction and advice of our Camera Crane Com- 
mittee, and taking advantage of the previous knowledge and experi- 
ence gained in the use of the small cranes, a staff engineer designed a 
crane which was acceptable to all of the studios. 

Normally, we would provide manufacturing firms with performance 
specifications or a complete design, and they would manufacture and 
sell directly to the industry. This would complete the Council's proj- 
ect. Equipment required by studios, however, is often so specialized 
that manufacturers are reluctant to produce the item for sale on the 
open market. Such was the case with the crane. We were unable to 
find a firm willing to undertake the manufacture because of the risk 
involved compared to the possible market for such specialized equip- 
ment. The Council, therefore, found it necessary to correlate studio 
orders and arranged for the manufacture of an initial order of twenty- 
five. 



, 1948 RESEARCH COUNCIL 423 

As a part of the crane project, we are building a prototype of a dual 
camera head and have in the design stage a location carriage for the 
crane. 

Some other short-term projects under consideration are polonium 
for static elimination, red-sensitive photoconductive tubes, materials 
and equipment for simulating fog, more efficient wind machines, du- 
plication of color stills for stereopticons, and nonfadirig dye agents for 
plaster. 

In conclusion, I should like to point out first, that we are engaged 
in applied research, rather than in the opposite extremes of pure re- 
search or manufacture. We are working closely with research groups 
in and outside the industry and bringing to their attention problems 
of importance to our industry. 

Second, we are acting as a liaison between studios and suppliers. 
On one hand suppliers are using the Council to distribute directly to 
those concerned in the studios, information on new products. This 
informational service is set up and working. On the other hand we are 
correlating studio needs and desires and presenting such information 
to the suppliers. This procedure saves time, standardizes methods 
and practices, and results in better and less expensive equipment. 

Third, our effort is an industry effort. The Research Council has 
been set up by this industry for this industry. To quote Mr. Freeman, 
our chairman, "we have in the motion picture industry one of the 
largest reservoirs of competent and experienced engineering and 
technical personnel of any industry." The Council needs the benefit 
of this experience and knowledge. We not only welcome, but request 
your help, your suggestions, and your advice. 



Use of 16- Mm Motion Pictures 
for Educational Reconditioning* 

BY EDWIN W. SCHULTZ 

ARMY MEDICAL CENTER, WASHINGTON, D. C. 



Summary This paper will cover in a general way some of the things 
which have been done at the Walter Reed General Hospital with 16-mm 
films and at the same time will offer a few suggestions which, it is believed, 
will help to improve the motion picture industry so far as the 16-mm non- 
theatrical field is concerned. 



REAT IMPETUS has been given to the development of visual educa- 
tional methods as a result of the demand for accelerated training 
programs in the Armed Services. Training films, documentary re- 
ports, and general informational subjects to aid in the orientation of 
the soldier have established the value of motion pictures in supple- 
menting other media of learning; also research studies have shown 
the motion picture to be one of the most popular forms of entertain- 
ment and diversion among American servicemen. 

Within each hospital there are wide opportunities for educational 
reconditioning personnel to develop programs well implemented with 
carefully selected screen subjects that will aid in the psychological re- 
conditioning and contribute to the resocialization of individual 
patients. 

The film program must be planned in a way that will accomplish 
the following four objectives: 

(1) To contribute to the individual's personal adjustment by pro- 
viding information and fostering understanding of the hospital pro- 
gram and providing local orientation to restore confidence, establish 
respect, and develop a "sense of belonging." 

(2) To develop the concept that the struggle in which we were en- 
gaged required the total and continued effort of all, not only to win in 
the field but also to secure a society dedicated to the principles of 
democratic living. 

(3) To offer occupational information co-ordinated with the pro- 
grams of counseling and vocational guidance to aid in the exploration 

* Presented October 15, 1945, at the SMPE Convention in New York. 
424 OCTOBER, 1948 JOURNAL OF THE SMPE VOLUME 51 



FILMS IN REHABILITATION 425 

of job opportunities and benefits available to the prospective dis- 
charged soldier, should he require further education or vocational 
rehabilitation. 

(4) To supplement the content of specific courses of instruction 
offered in educational reconditioning or the convalescent training 
program. 

The building of a film program, that will adequately serve the ob- 
jectives of reconditioning, demands skillful balancing of films with a 
serious purpose and those of a diversional and entertaining nature. 

In order to carry out the film program as outlined, the Surgeon 
General of the Army established a Visual Aids Center at the Walter 
Reed General Hospital in Washington, D. C. It is the responsibility 
of the Center to (1) provide necessary films, projectors, screens, and 
other film equipment; (2) train projectionists and maintain equip- 
ment; (3) determine all film sources and secure films for the programs 
from all fields, insuring proper screening technique; (4) assist in the 
proper utilization of films in the reconditioning, information, and 
educational programs; (5) assist hi the adoption and improvisation 

of equipment for all such purposes in the hospital; (6) advise military 
personnel of the hospital on the most effective ways of using motion 
pictures and other visual aids in the programs; and (7) recommend 

to the Surgeon General production of visual material which can be 
utilized in all Army Service Forces Hospitals to further recondition- 
ing activities. 

So far has been outlined the plan for the use of the 16-mm film in 
the reconditioning program. Now let us talk a little about how it 
i is used at Walter Reed General Hospital and later some of the 
problems which confront us. 

First, the theme at Walter Reed Hospital has been "If the man 
cannot come to the movies, take the movies to the man." In other 

words, we believe that, what we in the hospital know as the "class 
four" or bedfast patient is just as entitled to see entertainment and 
educational movies as the "class three" or ambulatory man, who can 
go to the places where motion pictures are shown. In order to do this 
portable carts equipped with 16-mm sound projectors and screens 
have been provided. These can be wheeled into the wards and films 
shown for the men confined to their beds. These units, in the hands 

1 of trained projectionists, give remarkably near-professional shows. 

1 The lighting is good and the sound adequate. Audiences number 

from a dozen or so up to 50 or 60 depending on the number of men 



426 SCHULTZ October 

In the ward. The reconditioning service confines its shows to educa- 
tional, documentary, and vocational-type films primarily, while the 
Red Cross furnishes the full-length entertainment features. 




Fig. 1 Cabinet- type booth for the 16-mm projector 
which is in use at the Walter Reed General Hospital. This 
booth is on the balcony of the Auditorium of the Red 
Cross building at the hospital. The amplifier of the 16-mm 
projector is jacked into the permanent 35-mm sound sys- 
tem on the stage which makes it possible to show 16-mm 
sound pictures on the big screen on the stage and get maxi- 
mum tone qualities. This provides a more or less per- 
manent setup in the auditorium for showing 16-mm pic- 
tures at any time to the ambulatory patients. 

Second, a daily information-education program is conducted in a 
large theater auditorium which is attended by wheel-chair, crutch, 
and walking patients. These programs usually last an hour and are 
package or unit programs, a week being assigned to a subject during 



1948 FILMS IN REHABILITATION 427 

which outstanding speakers are brought in to discuss the subjects 
along with which films are shown dealing with the various phases of 
the subject. The sessions usually draw large audiences and the 
program is broadcast over the hospital radio system so that men in 
bed can hear it over their individual bedside headsets. 




Fig. 2 A discarded wheeled stretcher has been utilized 
to make a cart for carrying complete projection unit to the 
wards for ward showings of films at the Walter Reed 
General Hospital. The addition of a bottom shelf and 
the wooden top converts the stretcher into an easily 
handled, practically silent, rolling cart. There's suf- 
ficient room for projector, amplifier, speaker, screen, 
films, and extra reels and is easily handled by one man. 

- The third place where films are used is in the various crafts and 
vocational shops. Among these shops is included carpentry, music, 
art, leather tooling, and typewriting and business machines. Films 
covering many phases of work in these crafts are shown to the patients 
in a specially provided "little theater." While no attempt is made to 
go into actual vocational training, an effort is made toward doing 
exploratory work to help the patient find his fitness for a certain 



428 



SCHULTZ 



October 



craft or trade, and at the same time occupy his mind while the| 
medical officers are curing him of his physical ills. Here we can! 
only touch on the immense problem which we faced, and which still ] 
faces us, and the progress that has been made. It will require a I 
visit to Walter Reed Hospital to see how the job is being done. 

Films are being employed in the treatment of the neuropsychiatric I 
patients with very good results. Men mentally disturbed react! 

extremely well toward films which 
are shown them, and they have! 
motion pictures almost every day. I 
As an indication of the use of I 
16-mm films at Walter Reed Hos- 
pital, it might be well to give 
you the figures on utilization 
during the 3-month period of 
June, July, and August, 1945. 
During those three months, 598 
films were shown with a total 
of .1470 showings and a total 
attendance of 46,760. 

Among the problems which 
were faced in bringing a film 
program to the patients, was 
first, the lack of the right kind 
of 16-mm films available. Of 
the many film subjects that are 
available today in 16-mm sound, 
a majority of them are unsuitable, 
the sequences are bad, the pho- 
tography poor, and the sound inadequate. The films made by the 
Signal Corps Army Pictorial Service, were all excellent but were 
unsuited for use in the hospital as they were filmed for military 
training and our patients are through with that phase of their career. 
The Surgeon General's Office started work on the evaluation and 
procurement of available 16-mm films suitable for hospital use, but 
only a few were acceptable. That office also launched certain pro- 
ductions. The Visual Aids Center at Walter Reed started a campaign 
to borrow from any source such pictures as could be used in these 
programs. We faced the rental-fee problem right off, but we were 
not in a position to pay rentals on all the films we wanted to use. In 




Fig. 3 A class in auto mechanics 
see a film on first echelon maintenance 
in the auto shop of the Educational 
Reconditioning Section of the Walter 
Reed General Hospital. More than 
30 films are used continually by this 
course during classes. 



1948 FILMS IN REHABILITATION 429 

most cases the firms having 16-mm films were most co-operative and 
we secured the use of literally hundreds of prints with no charge other 
than transportation. 

In speaking of the lack of quality subject in 16-mm, let me make 
it clear that I am not speaking of the 16-mm Hollywood feature 

I pictures which have been released, but those of an educational or 

^documentary nature. It has been my experience that there is a 
very definite need for more high-class, well-produced films of an 
educational and documentary type. It offers a great field, and 
educational institutions consistently will demand a better quality 
product; which is where an organization such as the Society of 
Motion Picture Engineers can play a very definite part. Regardless 

i of what some of the 35-mm producers want to believe, the sub- 
standard 16-mm film is here to stay and the sooner all men in the 

L industry realize it and make an effort to see that only the best quality 
16-mm films are produced, the better off the entire industry will be. 
It may be worth while to look ahead somewhat and consider the 
great need the Veterans' hospitals will have for 16-mm films to carry 
on the work of rehabilitation, resocialization, and vocational training 
which eventually will be their responsibility. The work that is 
being done is small, compared to what faces the Veterans Adminis- 
tration in the years to come. While only a very small percentage 
of the total number of veterans of World War II are in our hospitals, 

' later there will be tens of thousands seeking the help of the Veterans 
Administration. 

Should we not look ahead and be prepared, and not face a "Pearl 
Harbor" situation with respect to this matter? 
Should we not use the experience we have gained and the time we 

i. now have to prepare, rather than procrastinate and have to make a 

i mad dash later? 

If pioneer groups such as the SMPE and other agencies, both 

i private and governmental, will carry on while the momentum is 
rapid, there will be much accomplished; certainly, the future outlook 
for 16-mm educational films was never brighter. 

The third and last phase is that of projection equipment and 
the shooting of pictures in 16-mm sound rather than the 35-mm 
to 16-mm reduction method. 

Considerable difficulty has been experienced during the war 
years with 16-mm projection equipment. Many of the available 
projectors were made so rapidly and out of such poor material that 



430 SCHULTZ 

maintenance became a major problem because of rough handling 
and lack of well-experienced operators. Again a scarcity of repair 
parts and good repairmen was a problem. The remarkable fact 
is that they stood up as well as they did. 

Now that the war is over, there should be an over-all improvement 
in the quality of projection production, servicing, and a lowering 
of costs, not only in the purchase prices of new projectors but in 
the cost of replacement parts and maintenance. These facts are 
mentioned as it is believed that 16-mm projection equipment must 
be priced at such a figure as to make projectors within the reach of 
other than the wealthy individual, the school, or the industrial 
concern with unlimited funds. 

Sixteen-millimeter projection equipment also must be improved to 
make maintenance a minor problem for schools and industrial con- 
cerns and improvements made in the amplifier systems in order 
to give better quality sound. If the quality of the equipment can 
be improved and the cost reduced, the future of the 16-mm film 
as an educational medium is assured. The next aim should be an 
improvement in 16-mm productions for educational use. All 16- 
mm educational films should be filmed in 16-mm with original 
sound to get away from bad effects caused in reduction of prints from 
35-mm film. This will not only mean a reduction in cost but will 
mean better prints in my belief. 

A great field seems open to enterprising business concerns willing 
to sponsor good-quality educational films as an advertising medium, 
provided they do not ruin the sustained interest by too much ad- 
vertising. This is especially true with the outlook, of present-day 
trends as regards television, since already a number of 16-mm films 
have been produced and televised. 

ACKNOWLEDGMENT 

The photographs used to illustrate this article were furnished by 
The Visual Aids Center, Army Medical Center, Washington, D. C. 



Report of 

Studio- Lighting Committee 



THIS REPORT describes motion picture studio-lighting power 
sources and completes a series of reports covering all phases of 
studio-lighting equipment. 1 " 4 

Direct-current motion picture studio-lighting power sources may 
be divided into three general types: (1) Permanent installations con- 




Columbia Pictures Corporation 

Fig. 1 Main generator room. 500-kilowatt General Electric motor-generator 

sets. 



sisting of motor-generator sets usually installed in a centrally located 
powerhouse and with suitable underground cable connecting them to 
the stages. (2) Portable motor-generator sets mounted on trucks or 
trailers which may be located outside stages for extra power where 
heavy loads are used, or which may be sent out on location. (3) In- 
ternal-combustion engine-driven generators which find their greatest 
use on locations where power from electric lines is not available. 



* Original manuscript received October 11, 1947. 

OCTOBER, 1948 JOURNAL OF THE SMPE VOLUME 51 



431 



432 



STUDIO-LIGHTING REPORT 



October 



oo 







CQ 

I 

H 

W 

I 

h- 1 O 

gs 

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Generato 



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^.s.g- 










. 

lillil! Illiil 



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1948 STUDIO-LIGHTING REPORT 433 

The types of studio-lighting power sources in present use are legion 
and it is outside of the scope of this report to catalog all of them. 
Table I gives the characteristics of typical units and includes such 
factors as desired ripple characteristics which may not be present in 
some equipment, but which are desirable to minimize the necessity of 
choke coils and niters when using carbon-arc lamps. 5 



Metro-Goldwyn-Mayer Studios 

Fig. 2 Portable motor-generator set, 300 kilowatts as in No. 3, Table I. 





Metro-Goldwyn-Mayer Studios 

Fig. 3 Same as Fig. 2 except unit in closed position. 

Compound-wound generators are used because of their ability to 
maintain voltage under widely fluctuating load conditions. Com- 
pound-wound generators may be, and often are, paralleled by the use 
of an equalizer, or low-resistance connection, between the machines 
which places their series fields in parallel. However, in order to ac- 
complish the foregoing the generators must be of identical, or similar, 
electrical characteristics. Either similar or dissimilar compound 



434 



STUDIO-LIGHTING REPORT 



October 




Walt Disney Productions 

Fig. 4 Portable internal-combustion engine-driven generator. 150-kilo- 
watt generator, 290-horsepower motor, 1400 amperes, Thiotron automatic 
voltage control. 

the use of automatic voltage 



by 



generators may be paralleled 
regulators. 

Permanent-installation motor-generator sets are mounted on con- 
crete bases. Approximate weights for one known installation are 
34,000 pounds for the 500-kilowatt set and 20,000 pounds for the 
300-kilowatt set without bases. 




Fig. 5 Same as Fig. 4. 



Walt Disney Productions 

Control panel. 



1948 



STUDIO-LIGHTING REPORT 



435 



Drive motors on portable motor-generator sets are usually made 
for operation on more than one voltage and those used in Hollywood 
are capable of operation at both 50 and 60 cycles. 

Internal-combustion engine-driven generator sets may be made up 
of any combination of generator and gas or diesel engine provided the 
generator characteristics conform to the speed-horsepower charac- 
teristics of the engine. It is desirable that the generator be capable 







Mole-Richardson Company 

Fig. 6 A part of fleet of rental internal-combustion engine-driven generators. 
Rated at 1400 amperes, 120 volts, 230-horsepower engine. 

of maintaining voltage with approximately 65 per cent load at around 
65 per cent of its rated speed. 

These sets usually have a capacity of between 750 and 1400 am- 
peres at 125 volts. For design estimates a basis of 5 amperes of gen- 
erator output per engine horsepower may be used. Engine horse- 
power so estimated includes that necessary to drive the water pump, 
fuel pump, and other usual engine accessories. As a protective 
measure, engine horsepower should be below that capable of driving 
the generator at an injurious load. 

Incandescent lamps may be, and sometimes are, operated on alter- 
nating current to relieve a heavy direct-current load. This practice 
is not common, however, because of the difficulties encountered with 
two types of power being delivered through similar distribution sys- 
tems on the sets. 

Mercury-arc rectifiers have been considered as a direct-current 
source of power for motion picture studio lighting but no installations 
have been made to date. 6 



436 



STUDIO-LIGHTING REPORT 




Westinghouse Electric Corporation 

Fig. 7 Warner Brothers Studios powerhouse, 500-kilowatt Westinghouse 

motor generators. 

REFERENCES 

(1) R. G., Linderman, C. W. Handley, and A. Rodgers "Illumination in mo- 
tion picture production," /. Soc. Mot. Pict. Eng., vol. 40, pp. 333-368; June, 
1943. 

(2) "Report of the Studio-Lighting Committee," J. Soc. Mot. Pict. Eng., vol 
45, pp. 249-261; October, 1945. 

(3) "Report of the Studio-Lighting Committee," /. Soc. Mot. Pict. Eng., vol. 
47, pp. 113-118; August, 1946. 

(4) "Report of the Studio-Lighting Committee," /. Soc. Mot. Pict. Eng., 
vol. 45, pp. 279-289; September, 1947. 

(5) B. F. Miller, "A motion picture arc-lighting generator filter," J. Soc. Mot. 
Pict. Eng., vol. 41, pp. 367-374; November, 1943. 

(6) L. A. Umansky, "Power rectifiers for studio lighting," J. Soc. Mot. Pict. 
Eng., vol. 45, pp. 414-441; December, 1945. 



STUDIO-LIGHTING COMMITTEE 

(1947) 



J. W. BOYLE 
R. E. FARNHAM 



C. W. HANDLEY, Chairman 
KARL FREUND 
M. A. HANKINS 
C. R. LONG 



W. W. LOZIER 
D. W. PRIDEAUX 



, 



roposed 16-Mm and 8-Mm 
Sprocket Standards 

THE PAPER entitled "Proposals for 16-Mm and 8-Mm .Sprocket 
Standards/' by J. S. Chandler, D. F. Lyman, and L. R. Martin, 
was published in the June, 1947, issue of the JOURNAL OF THE SMPE 
for the purpose of inviting comment on the work that has been done 
on the design of sprockets. Discussion by letter was received from 
Mr. E. W. Kellogg of the Radio Corporation of America in which he 
questioned the propriety of the sprocket proposals as American 
Standards. Mr. Kellogg's letter was not received in time to be pub- 
lished at the same time as the paper; however, a notice appeared 
with the paper stating that Mr. Kellogg's discussion and a reply 
from the authors would appear at a later date. These two letters 
are published here. 

JOHN A. MAURER 
Engineering V ice-President 

MR. E. W. KELLOGG: Much as I admire the work which the authors have done, 
I think that the title given the paper is not well chosen. There are, of course, 
many possible titles. One might be "A Method of Designing Sprocket Teeth for 
Minimum Flutter." We do not see any reason for suggesting that the resulting 
tooth shape be made a "Standard." In fact, the fundamental purpose of Stand- 
ards is to make interchangeability possible. Obviously films must be inter- 
changeable so that they will run on all machines, but if a manufacturer puts out a 
machine which performs well with a standard film, and the film is not subjected 
to undue wear, and his customers are happy, he has complied with all of the con- 
ditions which are important. Subject to the above conditions we might say that 
it is no one else's business what shape tooth he uses. The occasion for attempting 
actually to standardize sprocket designs would come only when and if it becomes 
the practice of projector and camera manufacturers to procure their sprockets 
from certain sprocket manufacturers who specialize in stock designs which are 
interchangeable and are to be used by various equipment manufacturers. We do 
not foresee such a development. 

There is, on the other hand, a definite objection to giving the Society's official 
sanction to a specific design when sprocket teeth of other designs are in wide, suc- 
cessful use. The argument against such standardization has been well stated in 
correspondence between members of the present Subcommittee on "8-Mm and 
16-Mm Projector Sprocket Standards." Messrs. Sachtleben and Isom of RCA 
pointed out 

that while the plan to extend the usefulness of existing sprocket-design infor- 
mation, by putting it into the form of formulas including several of the vari- 
ables of projector design, was highly commendable, standardization of design 

OCTOBER. 1948 JOURNAL OF THE SMPE VOLUME 51 437 



438 DISCUSSION October 

on the basis of such formulas was not desirable. This was because the grow- 
ing prestige of standardization automatically would put a projector employing 
nonstandard sprockets at a competitive disadvantage; whereas it could be 
possible that under actual test the nonstandard sprockets would exhibit 
superior performance. 

Mr. Isom emphasized 

from his experience in the educational field, the prestige and authority stand- 
ards enjoy among persons charged with the responsibility for institutional 
purchases. These people make their choices on the principle of elimination , 
and seize upon published standards as their aid and authority in this process. 

For a number of years the Society has published information on the basis of 
which a designer can produce sprocket teeth which have been found to be 
satisfactory. 

These designs have been published under the caption "SMPE Standards." 
While we hold to the position that such information should be designated as a 
ommended design procedure rather than a standard, we would not hesitate for 
moment to say that the information has been useful to the industry. If tl 
Society wishes to continue to call any sprocket- tooth design "Standard," it w< 
be justified in changing to a new standard only if the new design had been showi 
after prolonged use, to be definitely superior. We think for the present tl 
Society should go no farther than to include it among acceptable designs and 
experience provide the ultimate answer as to superiority. Although RCA engi- 
neers are not at the present time in a position to pass on the performance of the pr 
posed tooth, we may say the following in regard to the tooth design which we havt 
used practically without change for a good many years. This design corresponds 
very closely to the old SMPE "Standard" as published in 1934. 

Many thousands of projectors have been in service for years in the Army and 
elsewhere where the service is severe. In all this experience practically no com- 
plaints have been received of trouble with sprockets. Mr. del Valle has given me 
the story of a series of tests of film life made, for the most part, during the summer 
of 1944. Twelve-foot loops were run through our projectors (including the inter- 
mittent) in a setup having a tensioning roller which put about 4 ounces tension 
each on the supply and takeup lines. The average life of a number of loops of 
film run in different machines, properly adjusted, was of the order of 25,000 pas- 
sages, and one loop ran 86,000 passages before slight cracks appeared at the cor- 
ners of the perforations. It cannot be said that this was a case of perfect fit be- 
cause the test of this loop extended over many weeks during the summertime, and 
there must have been some shrinkage. 

If we compare a tooth designed for a typical case, according to the formula given 
in this paper, with one designed according to the previously recommended prac- 
tice, there is a striking difference in that the sides of the new tooth slope much 
more near the bottom, whereas the sides of the old tooth start more nearly ver- 
tical. The effect of this difference would be to give the film much more tendency 
to climb up the tooth or to make it necessary to resort to special measures to hold 
the film down against the sprocket body. It does not seem to me practical to 
force the film all the way down. Shoes must offer sufficient clearance to permit 



1948 PROPOSED SPROCKET STANDARDS 439 

splices to pass. The film can still climb 5 or 6 mils up the tooth if it wishes to, and 
even ride at that position throughout its engagement with the sprocket. 

We might expect then, in spite of the very well worked-out theory, that the 
new tooth, which under ideal conditions would minimize flutter, would give more 
erratic results, or require greater niceties of design and C3nstruction in order to 
realize the possible benefit. Although the old tooth undoubtedly would give more 
nutter at the sprocket than the new tooth when working at its best, we depend on 
mechanical filtering to take out the flutter, and it is a serious question whether 
other desirable properties should be sacrificed to reduce flutter at the sprocket. 
The actual 24-cycle or 96-cycle flutter is very effectively filtered. Much harder to 
filter out would be variations in the manner in which the film rides on the sprocket 
which might result in random phase shifts at the sprocket, having components of 
much lower frequency. 

While my remarks are based largely on theory and it may well be that the 
authors of the paper have gotten excellent results from their sprockets, I think 
that there is abundant reason for a very cautious attitude on the part of the 
Society with regard to recommending the new design as superior, or of giving it 
the special sanction of calling it "Standard," especially when the former designs 
are giving such excellent satisfaction. 

There are special cases where mechanical filtering is not employed, such as 
sprocket-type printers and certain recorders, and for these applications the 
authors' approach to the problem of minimizing flutter deserves careful 
consideration. 

J. S. CHANDLER, D. F. LYMAN, AND L. R. MARTIN: The authors are grateful 
to Mr. Kellogg for the careful attention he has given this subject, and for his 
comments, which serve to re-emphasize some of the important points in the 
paper. We agree that the desirability of standardizing sprockets on. the basis 
of insuring good performance is open to question, since the usual function of 
standards is to provide for interchangeability of parts. But the present ASA 
standard for 16-mm sprockets, Z22. 6-1941, deals with dimensional specifications 
that are related not only to interchangeability but also to performance. We 
agree also with Mr. Kellogg's statement that the information in the present 
standard has been useful to the industry. It has been realized for some time, 
however, that the existing standard is inadequate in that the same tooth profile 
is recommended for all sprockets, regardless of the number of teeth on the sprocket. 
Moreover, no account is taken of such related and dependent factors as the range 
of film shrinkage for which accommodation is to be made and the shape of the 
path followed by the film as it approaches and leaves the sprocket. If for these 
reasons the current standard is allowed to lapse and no substitute is made avail- 
able, the industry will soon be keenly aware that it lacks an authoritative source 
of information on this important subject. 

It was largely because of these latter considerations that a committee on 
sprockets was formed and the project leading to the present proposals was insti- 
gated. One point should be emphasized: the profile recommended for the 
tooth is designed to give maximum film life, not necessarily minimum flutter. 
The fact that the recommended tooth would, theoretically at least, result in less 
flutter than would be obtained with the alternative shape shown in Fig. 9 of our 
paper is incidental; it follows from the basic principle that if the acceleration 



440 DISCUSSION 

of the film is kept low as it strips off the driving tooth, the impact of the film 
against the next tooth is less severe. 

As Mr. Kellogg points out, the recommended tooth slants more at the base 
than does the tooth in the existing ASA standard. This criticism was offered 
early in the work on the proposals, and that is why the alternative profile was 
included in Fig. 9. Experiments have demonstrated that the flexing of the 
film in the region of the loaded edge of the perforation, rather than impact loading, 
determines the life of the film. If further studies show that the alternative tooth 
shape, which is steeper at the base but more sloping at the tip, affords longer 
film life, it should be the one that is recommended and the formulas should be 
changed accordingly. 

The purpose of submitting this proposal is to encourage more trials by a number 
of investigators, since sprocket specifications resulting in optimal performance 
can be determined only after extensive tests. The form of the proposal is such 
that the equations can be altered readily to make them comply with the results 
of such tests, the importance of which cannot be overemphasized. 



Incorporation of American Standards Association 

rpiHE AMERICAN Standards Association became the American Standards 
J- Association, Incorporated, August 2, 1948, through incorporation under the 
laws of the State of New York. This is the third in a series of changes which have 
consistently recognized the enlarging scope of the Association's work. 

Organized in 1918 as the American Engineering Standards Committee, a co- 
ordinating committee for the standardization work of five of the country's im- 
portant technical societies, the scope and organizational setup were soon broad- 
ened to include associations and government agencies. This led to the extension 
of the work into the field of safety standards. In 1928, an entire reorganization 
took place, changing the Committee into a full-fledged "American Standards 
Association," the nation's clearing house for standards and the United States 
medium for international contacts on standardization. The present change to an 
incorporated Association again recognizes the enlarged activities and responsibili- 
ties of the organization, giving it and its members the protection and benefits 
which corporation law affords and which is considered essential in the light of the 
scope of the Association's activities. 

Bills seeking Federal incorporation are now before Congress, having been intro- 
duced in the House by the Honorable Kenneth B. Keating of New York, and in 
the Senate by the Honorable Ralph Flanders of Vermont. 

The Association's co-ordinating functions now extend to standards in the 
mechanical, electrical, building, photographic, mining, safety, and consumer-goods 
fields, as well as such general work as that on office equipment and abbreviations 
and symbols for use in engineering and scientific literature. 

Frederick R. Lack, vice-president, Western Electric Company, is president of 
the Incorporated Association. Vice-Admiral G. F. Hussey, Jr. (United States 
Navy, retired), is secretary and adminstrative head, and Cyril Ainsworth is tech- 
nical director. 




THOMAS ARMAT 



THOMAS ARMAT, pioneer inventor of the motion picture projec- 
tor, who died on September 30, 1948, received a special award 
this year from the Academy of Motion Picture Arts and Sciences 
for his contributions to the development of the motion picture. 
The statement of the Academy reads as follows: 

"Academy Special Award to Thomas Armat, one of the small 
group of pioneers whose belief in a new medium, and whose 
contributions to its development, blazed the trail along which 
the motion picture progressed, in their lifetime, from obscurity 
to world-wide acclaim/' 

In 1946, on the occasion of the Fiftieth Anniversary of the first 
exhibition of motion pictures in a theater, Mr. Armat was awarded 
a Citation by the Society of Motion Picture Engineers in recogni- 
tion of his distinguished inventions which were outstanding features 
of his first projecting machine. 

Mr. Armat was born in Fredericksburg, Virginia, on October 26, 
1866, and in February, 1896, he demonstrated a motion picture 
projector of his own design to Thomas A. Edison at his laboratory 
in West Orange, New Jersey. This projector, known then as the 
Vitascope, was the first to incorporate a loop-forming means and 
a longer period of rest and illumination than the time required to 
move the film from one frame to the next. These features were a 
major step in the development of modern motion picture projec- 
tors and were incorporated subsequently in most commercially 
successful projection machines. 

Mr. Armat was elected an Honorary Member of the Society of 
Motion Picture Engineers in October, 1935. 



LOUIS LUMIERE 

Louis LUMIERE, 83, foremost Frenchman of the cinema, died 
on June 6, 1948, at Bandol on the Riviera. 

M. Lumiere and his brother, Auguste, were among the pioneers 
outside the United States who developed the possibilities of the 
motion picture Kinetoscope. On December 28, 1895, they opened 
an exhibition in the basement of the Grand Cafe in Paris. This 
marked the beginning of commercial motion picture exhibition in 
France. 

The Lumieres were manufacturers of photographic materials at 
Lyon, in France. They set to work, as did so many others, to join 
the Kinetoscope's peep-show pictures with the magic lantern to 
achieve projection. Lacking film base, which could only be had 
from their American competitor, Eastman, they sent to New York 
for a makeshift material, strips of celluloid from the American Cel- 
luloid Company. Being economically minded, also, they cut the 
rate of motion picture photography from Edison's 48 frames a second 
to 16 frames. 

After the demonstration of his motion picture camera Lumiere 
experimented with color photography and developed a number 
of photographic appliances. So outstanding were his contribu- 
tions that on April 22, 1935, he received a tribute from the Motion 
Picture Producers and Distributors. 

M. Lumiere was, for a short time, a member of Marshal Petain's 
advisory council of State. He was honorary president of the 
French Chamber of Cinema, a member of the French 
Academy of Sciences, a grand officer in the Legion of Honor, and an 
Honorary member of the Society of Motion Picture Engineers. 

TERRY RAMSAYE 



THAD C. BARROWS 

THAD C. BARROWS, 59, president of Boston Local 182 from 1918 
until 1947, died as a result of a heart attack on June 2, 1948. 

Until the day of his death he was actively engaged in his craft 
in Boston's Metropolitan Theater, and his interest in technological 
developments in his work was unflagging. 

Recognition of his enthusiastic devotion to his field came in 
1929 when he was unanimously elected the first president of the 
Projection Advisory Council, a national organization which con- 
tributed greatly to the industry during the difficult years of transi- 
tion to sound motion pictures. He was an Active member of the 
Society of Motion Picture Engineers for 20 years. 

His sincerity, courage, and honesty won the affection and respect 
of all who knew him. 



Book Reviews 



Enlarging Technique of the Positive, by C. I. Jacobson 

Published (1948) by the Focal Press, Inc., 381 Fourth Ave., New York 16, N. Y. 
307 pages + xx pages + 9-page index. 77 illustrations. 5 : /4 X 7*/2 inches. 
Price, $3.50. 

The culmination of the photographer's work is the print. Involved in its 
preparation is a whole series of events including materials, techniques, and 
equipment. These are the negative, the printing media, the enlarger, the proc- 
essing technique, and the aftertreatment. Involved also are psychophysical 
and physiological aspects such as perspective and other distortions, definition, 
and visual acuity. All of these topics are treated in a chatty manner which makes 
for easy reading. As with the companion volume (see the review on "Develop- 
ing," by the same author, published in the July, 1948, issue of THE JOURNAL, 
page 105), the emphasis has been laid on description without the use of techni- 
cal language, and without the presumption of a technical background. And 
yet an adequate panorama of the field is given. 

The book will be valuable to all who desire to learn what is involved behind the 
scenes, when a camera record is converted into a final print. After a discussion 
of the negative material and its characteristics, as examplified by the negative 
to be printed, it goes on to treat in detail the printing media upon which the 
negative is to be copied. The first quarter of the book is therefore concerned 
with the materials used. But equipment and techniques are also involved in the 
cycle of events. The discussion of these incidentals is the subject matter of the 
remainder of the book. One obtains a working knowledge of the intricacies of 
enlarging equipment, of the various printing techniques, of tone separation 
processes, montages, and other matters. All in all it is a darkroom man's ele- 
mentary handbook on printing, and it will serve him as an excellent guide to help 
him solve old problems, or indicate to him new ones. 

JOSEPH S. FRIEDMAN 

Ansco 

Johnson City, New York 

Camera and Lens, by Ansel Adams 

Published (1948) by Morgan and Lester, 101 Park Ave., New York 17, N. Y. 
117 pages + 3-page index + viii pages. 77 illustrations. 6V4 X 9 1 /* inches. 
Price, $3.00. 

This book is the first in a series of six volumes on basic photography to be 
written by Ansel Adams. It is intended to acquaint the aspiring still photographer 
with those fundamentals of camera operation which the author considers essential 
in creative photography. However, there are six short chapters pertaining to 
darkroom layout and construction, darkroom equipment, the finishing room, 
negative storage, print storage, and print-display devices, none of which has 
much relation to the camera and lens. 

Mr. Adams is a photographer of repute. Some of his pictures rank among 
the best that have ever been produced, which attests his ability as a competent 
judge of aesthetic and photographic quality. It is unfortunate that he did not 

443 



444 BOOK REVIEWS 

choose to write a book in these fields, for he does not appear to be sufficiently 
versed in the technical aspects of photography to discuss them authentically. 
For a beginner's book too many terms are used before they are defined, and in 
some instances the terms are nowhere properly defined. For example, on page 5 
the term "parallax" is used without being defined, and not until page 15 is it stated 
that lens speed is expressed as //8, //3.5, etc., although this designation is used 
freely on previous pages. And in the chapter beginning on page 88, / number is 
improperly defined. 

Mr. Adam's discussion on composition is considerably better than one finds 
usually in the photographic literature. 

LLOYD E. VARDEN 

Pavelle Color 

New York 19, N. Y. 



Informational Film Year Book 1947 

Published (1947) by the Albyn Press, 42 Frederick St., Edinburgh 2, Scotland. 
174 pages. 25 illustrations. 5 X A X 8 3 /4 inches. Price, 10s. Qd. net. 

The rapid growth of the nontheatrical film in recent years is indicated clearly 
in several of the articles in this Film Year Book. Twelve short articles by well- 
known writers such as Paul Rotha, John Grierson, Andrew Buchanan, Forsythe 
Hardy, and Basil Wright comprise about one half of the book. Subjects discussed 
include documentary films, the conditions in nontheatrical film industry in 
America, the services rendered by the film in industry, the classroom film and 
films for children, and the use of films by the United Nations Educational, Scien- 
tific, and Cultural Organization (UNESCO). Summarizing the place of the non- 
theatrical film in the world today, Norman Wilson states, "It should be the aim of 
everyone who believes in democracy to make the freedom of the screen as much a 
reality as the freedom of the press." 

The latter half of this interesting volume contains a "Buyers' Guide" on new 
substandard apparatus; a group of stills from documentary films of the year; a 
list of the informational films of the year; also lists of film-producing organiza- 
tions, cine societies, studios, laboratories, libraries, manufacturers of cine appa- 
ratus, specialist cinemas, and film periodicals. 

GLENN E. MATTHEWS 

Kodak Research Laboratories 

Kodak Park, Rochester 4, New York 




Current Literature 



rpHE EDITORS present for convenient reference a list of articles dealing with 
J- subjects cognate to motion picture engineering published in a number of se- 
lected journals. Photostatic or microfilm copies of articles in magazines that are 
available may be obtained from The Library of Congress, Washington, D. C., or 
from the New York Public Library, New York, N. Y., at prevailing rates. 
American Cinematographer Ideal Kinema 

29, 6, June, 1948 14, June 10, 1948 

The Application of Motion Picture Consistency and Colour of Screen 



Technique to Television (p. 194) 
R. B. AUSTRIAN 

U. S. Navy Develops Super-Speed 
Cameras (p. 207) 

29, 7, July, 1948 

Photography for Television (p. 229) 
F. FOSTER 

29, 8, August, 1948 

Transition Lens for Television Cam- 
eras (p. 266) F. FOSTER 

The New "Spectra" Measures Color 
Temperature (p. 267) F. GATELY 

3000 Frames Per Second (p. 269) 

British Kinematography 

12, 5, May, 1948 

Sound-on-Film Reproducing Equip- 
ment: 

I. The Sound Head (p. 155) A. T 
SINCLAIR 

II. Electrical, Electronic and 
Acoustic Design (p. 159) H. J. 

O'DELL 

Television Production in Contrast to 
Film Production (p. 164) P. H. 

DORTE 

Electronic Engineering 

20, June, 1948 

A New Television Film Scanner 

(p. 174) 
Improving Circuit Diagrams (p. 175) 

L. H. BAINBRIDGE-BELL 

Electronics 

21, 7, July, 1948 

Design Factors for Intercarrier Tele- 
vision Sound (p. 72) S. W. SEELEY 

Photometry in Television Engineer- 
ing (p. 110) D. W. EPSTEIN 



Illumination (p. 20) R. H. CRICKS 
International Projectionist 
23, 6, June, 1948 
New Acetate Film for Release Prints 

(p. 5) C. R. FORDYCE 
Projection Factors of New Acetate 
Film (p. 6) 

23, 7, July, 1948 
Control of Sound-Film Reproduction 

(p. 5) R. A. MITCHELL 
New Century Sound Systems Fea- 
ture Fundamental Reproducer Ad- 
vances (p. 8) 
Television: How It Works (p. 10) 

W. BOUIE 

Theater Television: A General Sur- 
vey (p. 19) A. N. GOLDSMITH 

23, 8, August, 1948 
Television: How It Works. Pt. 2 

(p. 9) W. BOUIE 
Projector Progress in Great Britain 

(p. 18) H. HILL 
Proceedings of the I.R.E. 
36, 6, June, 1948 

The Application of Projective Geom- 
etry to the Theory of Color Mix- 
ture (p. 709) F. J. BINGLEY 

36, 7, July, 1948 

Avenues of Improvement in Present- 
Day Television (p. 896) D. G. FINK 
Radio and Television News 

40, 2, August, 1948 
The Recording and Reproduction of 
Sound. Pt. 18 (p. 49) O. READ 
RCA Review 

9, 2, June, 1948 

Motion Picture Photography of Tele- 
vision Images (p. 202) R. M. 
FRASER 

445 



Journal Exchange 



Dr. R. F. Nicholson wishes to dispose 
of a complete bound set of JOURNALS 
of the SMPE from January, 1928, 
through December, 1947. Prospec- 
tive purchasers should write to Dr. 
Nicholson at 230 Albany St., Cam- 
bridge 39, Mass., and mark the en- 
velope "Personal." 



The Society of Motion Picture Engi- 
neers has for sale certain back copies of 
the TRANSACTIONS and the JOURNAL, as 
listed below. 

TRANSACTIONS 

Numbers 3, 4, 10, 11, 12, 13, 14, 15, 17, 
19, 20, 21, 22, 23, 24, 25, 27, 28, 29, 
and 32 at $1.25 each; 33, 34, 35, and 
36 at $2.50 each; and 37 and 38 at 
$3.00 each. 



JOURNALS $1.25 each 
Entire Year: 1930, 1931, 1935, 1937, 

1942, and 1943. 
1932 no May 

1933 no May, June, October 
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April 

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August 

1946 no January, February, March 
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1948 all to date 

Send your order with remittance to 
the Society of Motion Picture Engi- 
neers, 342 Madison Avenue, New 
York 17, N. Y. 



35-MM AND 16-MM TEST FILMS 

for the manufacturer 

As an important tool for the design engineer and as a 
performance standard in quality control and inspection. 

for the dealer and serviceman 

To demonstrate new projectors and sound reproducers as 
well as to adjust equipment in service or in the process of 
being repaired. 

for 16- and 35-mm exhibitors 

To insure peak performance for those who maintain their 
own equipment. 

Twenty-nine different test films, both 16- and 35-mm are 
available for all purposes from the Society of Motion Picture 
Engineers and the Motion Picture Research Council. A catalog 
describing each in detail is available at no cost from the Society 
of Motion Picture Engineers, 342 Madison Avenue, New York 17, 
N. Y. 



446 



SECTION OFFICERS 



Atlantic Coast 



Chairman 

William H. Rivers 
Eastman Kodak Co. 
342 Madison Ave. 
New York 17, N. Y. 



Secretary -Treasurer 

Edward Schmidt 

E. I. du Pont de Nemours & Co 

350 Fifth Ave. 

New York 1, N. Y. 



Chairman 

R. T. Van Niman 
Motiograph 
4431 W. Lake St. 
Chicago 24, 111. 



Midwest 



Secretary-Treasurer 

George W. Colburn 

George W. Colburn Laboratory 

164 N. Wacker Dr. 

Chicago 6, 111. 



Pacific Coast 



Chairman 

S. P. Solow 

Consolidated Film Industries 
959 Seward St. 
Hollywood, Calif. 



Secre tary-Trea surer 

G. R. Crane 
21224 St. 
Santa Monica, Calif. 



Student Chapter 
University of Southern Calfornia 



Chairman 

Thomas Gavey 

1046 N. Ridgewood PI. 

Hollywood 38, Calif. 



Secretary-Treasurer 

John Barn well 

University of Southern California 

Los Angeles, Calif. 



Office Staff New York 



EXECUTIVE SECRETARY 

Boyce Nemec 
STAFF ENGINEER 

William H. Deacy, Jr. 



OFFICE MANAGER 
Sigmund M. Muskat 

JOURNAL EDITOR 
Helen M. Stote 



Helen Goodwyn 
Dorothy Johnson 



Beatrice Melican 



Thelma Klinow 
Ethel Lewis 



447 



Statement of the Ownership, Management, Circulation, Etc., Required by the 
Acts of Congress of August 24, 1912, as Amended by the Acts of March 3, 1933 
and July 2, 1946, of Journal of the Society of Motion Picture Engineers, published 
monthly at Easton, Pa., for October 1, 1948. 

State of New York ) 
County of New York j Sw 

Before me, a Notary Public in and for the State and county aforesaid, person- 
ally appeared Boyce Nemec, who, having been duly sworn according to law, de- 
poses and says that he is the Executive Secretary of the Journal of the Society of 
Motion Picture Engineers and that the following is, to the best of his knowledge 
and belief, a true statement of the ownership, management (and if a daily, 
weekly, semiweekly, or triweekly newspaper, the circulation), etc., of the aforesaid 
publication for the date shown in the above caption, required by the Act of August 
24, 1912, as amended by the Acts of March 3, 1933 and July 2, 1946 embodied 
in section 537, Postal Laws and Regulations, printed on the reverse of this form, 
to wit: 

1. That the names and addresses of the publisher, editor, managing editor, 
and business managers are: 

Name o/ Post Office Address 

Publisher, Society of Motion Picture Engineers, Inc., 342 Madison Ave., New 

York 17, N. Y. 

Editor, Helen M. Stote, 342 Madison Ave., New York 17, N. Y. 
Managing Editor, None. 
Business Manager, Boyce Nemec, 342 Madison Ave., New York 17, N. Y. 

2. That the owner is: (If owned by a corporation, its name and address 
must be stated and also immediately thereunder the names and addresses of 
stockholders owning or holding one per cent or more of total amount of stock. 
If not owned by a corporation, the names and addresses of the individual owners 
must be given. If owned by a firm, company, or other unincorporated concern, 
its name and address, as well as those of each individual member, must be given.) 
Society of Motion Picture Engineers, Inc., 342 Madison Ave., New York 17, N. Y. 
Loren L. Ryder, President, 5451 Marathon St., Hollywood, Calif. 

G. T. Lorance, Secretary, 63 Bedford Rd., Pleasantville, N. Y. 
Ralph B. Austrian, Treasurer, 247 Park Ave., New York 17, N. Y. 
No stockholders. 

3. That the known bondholders, mortgagees, and other security holders 
owning or holding one per cent or more of total amount of bonds, mortgages, or 
other securities are : (If there are none, so state.) 

None. 

4. That the two paragraphs next above, giving the names of the owners, 
stockholders, and security holders, if any, contain not only the list of stockholders 
and security holders as they appear upon the books of the company but also, 
in cases where the stockholder or security holder appears upon the books of the 
company as trustee or in any other fiduciary relation, the name of the person or 
corporation for whom such trustee is acting,, is given ; also that the said two 
paragraphs contain statements embracing affiant's full knowledge and belief 
as to the circumstances and conditions under which stockholders and security 
holders who do not appear upon the books of the company as trustees, hold stock 
and securities in a capacity other than that of a bona fide owner ; and this aifiant 
has no reason to believe that any other person, association, or corporation has 
any interest direct or indirect in the said stock, bonds, or other securities than 
as so stated by him. 

5. That the average number of copies of each issue of this publication sold 
or distributed, through the mails or otherwise, to paid subscribers during the 
twelve months preceding the date shown above is : (This information is required 
from daily, weekly, semiweekly, and triweekly newspapers only.) 

BOYCE NEMEC, Exec. Secy., Business Manager. 
Sworn to and subscribed before me this 18th day of August, 1948. 

(Seal) Elisabeth J. Rubino 
Notary Public, Clerk's No. 2986, 
Queens County. Reg. No. 86-R-9 
(My commission expires March 30, 1949) 



Journal of the 

Society of Motion Picture Engineers 

VOLUME 51 NOVEMBER 1948 NUMBER 5 



PAGE 

Proposed Standards for the Measurement of Distortion in 

Sound Recording 449 

Magnetic Recording for the Technician DOROTHY O'DEA 468 

35-Mm Magnetic-Recording System EARL MASTERSON 481 

Optimum High-Frequency Bias in Magnetic Recording 

G. L. DIMMICK AND S. W. JOHNSON 489 

Variable-Area Recording with the Light Valve 

JOHN G. FRAYNE 501 

Variable-Area Light- Valve Modulator LEWIS B. BROWDER 521 

Nine Recent American Standards 534 

Section Meetings 549 

Book Reviews: 

"The Diary and Sundry Observations of Thomas Alva 

Edison" 
Edited by Dagobert D. Runes 

Reviewed by Terry Ramsaye 550 

"L'Annuaire du Cinema 1948 (Motion Picture Yearbook 
for 1948)" 

Published by Editions Bellefaye 551 

Current Literature : 552 

New Products . . 553 



ARTHUR C. DOWNES HELEN M. STOTE GORDON A. CHAMBERS 

Chairman Editor Chairman 

Board of Editors Papers Committee 

Subscription to nonmembers, $10.00 per annum; to members, $6.25 per annum, included in 
their annual membership dues; single copies, $1.25. Order from the Society's general office. 
A discount of ten per cent is allowed to accredited agencies on orders for subscriptions and 
single copies. Published monthly at Easton, Pa., by the Society of Motion Picture Engineers, 
Inc. Publication Office, 20th & Northampton Sts., Easton, Pa. General and Editorial Office, 
342 Madison Ave., New York 17, N. Y. Entered as second-class matter January 15, 1930, 
at the Post Office at Easton, Pa., under the Act of March 3, 1879. 

Copyright, 1948, by the Society of Motion Picture Engineers, Inc. Permission to republish 
material from the JOURNAL must be obtained in writing from the General Office of the Society. 
Copyright under International Copyright Convention and Pan-American Convention. The 
Society is not responsible for statements of authors or contributors. 



Society of 

Motion Picture Engineers 

342 MADISON AVENUE NEW YORK 17, N. Y. TEL. Mu 2-2185 
BOYCE NEMEC . . . EXECUTIVE SECRETARY 

OFFICERS 

1947-1948 

PRESIDENT EDITORIAL VICE-PRESIDENT 
Loren L. Ryder Clyde R. Keith 

5451 Marathon St. 233 Broadway 

Hollywood 38, Calif. New York 7, N. Y. 

PAST-PRESIDENT CONVENTION VICE-PRESIDENT 
Donald E. Hyndman William C. Kunzmann 

342 Madison Ave. Box 6087 

New York 17, N. Y. Cleveland, Ohio 

EXECUTIVE VICE-PRESIDENT SECRETARY 
Earl I. Sponable G. T. Lorance 

460 West 54 St. 55 La France Ave. 

New York 19, N. Y. Bloomfield, N. J. 

1948-1949 

ENGINEERING VICE-PRESIDENT FINANCIAL VICE-PRESIDENT 

John A. Maurer James Frank, Jr. 

37-0131 St. 426 Luckie St., N. W. 

Long Island City 1, N. Y. Atlanta, Ga. 

TREASURER 

Ralph B. Austrian 
25 W. 54 St. 
New York, N. Y. 

Governors 

1947-1948 

John W. Boyle Robert M. Corbin Charles R. Daily 

1207 N. Mansfield Ave. 343 State St. 5451 Marathon St. 

Hollywood 38, Calif. Rochester 4, N. Y. Hollywood 38, Calif. 

David B. Joy Hollis W. Moyse 

30 E. 42 St. 6656 Santa Monica Blvd. 

New York 17, N. Y. Hollywood, Calif. 

1948 

William H. Rivers S. P. Solow R. T. Van Niman 

342 Madison Ave. 959 Seward St. 4431 W. Lake St. 

New York 17, N. Y. Hollywood, Calif. Chicago, 111. 

1948-1949 

Alan W. Cook Gordon E. Sawyer 

4 Druid PI. Lloyd T. Goldsmith 857 N. Martel St. 

Binghampton, N. Y. Burbank, Calif. Hollywood, Calif. 

Paul J. Larsen 

Los Alamos Laboratory 
University of California 
Albuquerque, N. M. 

Section Officers and Office Staff listed on page 554. 



Proposed Standards 
for the Measurement of 
Distortion in Sound Recording* 

ORGANIZATION AND PLAN OF WORK 

ON OCTOBER 25, 1947, a meeting was held of the American Stand- 
ards Association Committee on Standards for Sound Re- 
cording, under the chairmanship of George Nixon of the National 
Broadcasting Company. On this committee the Society of Motion 
Picture Engineers was represented by J. A. Maurer, C. R. Keith, 
Otto Sandvik, and E. W. Kellogg, who was asked to assume the chair- 
manship of a subcommittee to recommend standards with respect to 
the measurement of performance characteristics and distortion in 
sound recording and reproducing systems. The membership of the 
subcommittee is as follows : 

EDWARD W. KELLOGG, Chairman 
RCA Victor Division 
Camden, N. J. 

W. S. BACHMAN G. T. LORANCE 

Columbia Recording Corporation General Precision Laboratories 

New York, N. Y. Pleasantville, N. Y. 

PETER CHRZANOWSKI R. A. LYNN 

National Bureau of Standards National Broadcasting Company 

Washington, D. C. New York, N. Y. 

L. C. HOLMES OTTO SANDVIK 

Stromberg-Carlson Company Eastman Kodak Company 

Rochester, N. Y. Rochester, N. Y. 

(r. B. MEYER HARRY SCHECTER 

Westinghouse Electric Corporation Air Materiel Command 

Baltimore, Md. Cambridge, Mass. 

K. B. LAMBERT R. R. SCOVILLE 

Metro-Goldwyn-Mayer Pictures Electrical Research Products 

Culver City, Calif. Los Angeles, Calif. 

W. H. OFFENHAUSER, JR. 
New Canaan, Conn. 

* Presented May 18, 1948, at the SMPE Convention in Santa Monica. 

NOVEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 449 



450 DISTORTION MEASUREMENT November 

The work had been carried on largely by correspondence, with one 
meeting held at ASA headquarters on January 21, 1948. The 
method for the most part has been for the chairman, with the help of 
the members, to attempt to ascertain what standards already exist, 
or what procedures are current, and then to formulate proposals for 
the subcommittee members to criticize or correct. The circular let- 
ters with proposals, discussions, and questions have also been sent to 
numerous qualified persons who are not members of the subcommittee, 
and many valuable letters have been received. It is appropriate to 
acknowledge here the thoughtful comments plus information re- 
ceived from Howard Chinn of the Columbia Broadcasting System, 
New York; R. C. Moyer of the RCA Victor Division, In- 
dianapolis; W. R. Furst, of Furst Electronics, Chicago; J. W. 
Bayliss and Kurt Singer of the RCA Victor Division, Holly- 
wood; John T. Mullin of W. A. Palmer Co., San Francisco (rep- 
resenting also views of Ampex Corporation, San Carlos, Calif.); 
J. K. Hilliard of the Altec Lansing Company, Hollywood; Captain 
R. Bennett of the Navy Electronics Laboratory, San Diego; H. H. 
Scott of H. H. Scott, Inc., Cambridge: S. J. Begun, of Brush De- 
velopment Company, Cleveland; and A. R. Morgan of the RCA 
Laboratories, Princeton. Few of the proposals here outlined have 
had final approval of the subcommittee membership for submission 
to the main committee, but it seems desirable to take advantage of 
the opportunity offered by the Spring Convention of this Society 
to obtain a wider consideration of the questions on whose answers 
any standards must depend. This method is similar to what the 
SMPE Sound Committee did last year in submitting their propo- 
sals on Flutter Standards in a report, for consideration by the entire 
Society membership. This afforded them the benefit of wide dis- 
cussion and many viewpoints before the proposals were taken up by 
the Standards Committee. We hope to have a similar experience 
with respect to the proposals submitted here. 

TYPES OF DISTORTION 

Distortion in reproduced sound may be broadly divided into four 
types. 

(1) Inaccuracies of pitch or frequency, especially fluctuations in 
pitch relative to the original, which are generally called "flutter" or 
"wow." 



1948 DISTORTION MEASUREMENT 451 

(2) Inequalities in the amplification of sounds 

(a) depending on their frequency (lack of flat frequency re- 
sponse) ; 

(b) depending on their amplitude (volume expansion or com- 
pression); 

(c) variations with time (fluctuations in level relative to original) . 

(3) Phase distortion. In the reproduced sound certain compo- 
nents of complex sounds are delayed with respect to others. Transient 
distortion due to equipment resonances is one type of phase distortion, 
in that energy is absorbed from the sound for a short period of time 
and then released. Irregularities in frequency-response characteris- 
tics (as, for example, peaks due to resonance) are nearly always ac- 
companied by phase distortion.* 

(4) Production of spurious sounds, not in the original 

(a) overtones, due in general to nonlinearity in the instantaneous 
(or dynamic) output-to-input relationship in one or more of 
the elements of the system; 

(b) beat tones, also due in general to nonlinearity, resulting in 
rectification, but also caused by proximity effects in the rec- 
ord as in high-frequency variable-area recording; 

(c) noise, generally divided into that due to hum, mechanical 
vibration, and microphonic elements, and that due to the 
granular character of the record, plus foreign particles and 
minor injuries or abrasions. There are also noises of ther- 
mal and tube origin. 

TOPICS COVERED 

The assignment of our subcommittee does not include attempting 
to set standards of performance, but only to recommend such stand- 
ards as can be agreed upon for the measurement of performance char- 
acteristics and distortion. This may, however, involve specifica- 
tions for the measuring equipment itself. 

Standardization in measurements has, for its main object, the en- 
abling of persons in different laboratories to check and compare meas- 
urements; but a second and no less important object is to prevent 

* If phase distortions of this kind produce any audible quality changes, they are 
usually so overshadowed by the variations in response as to be of secondary 
importance. Moreover, measures which correct the response irregularities usu- 
ally also correct the phase distortion. 



452 DISTORTION MEASUREMENT November 

the misunderstandings which result from use of different systems, 
and especially from use of the same term with different understand- 
ings of its meaning. In many cases it may not be possible to get 
people in various organizations to adopt a single standard method of 
making tests and, when this situation is encountered, it still should 
be possible to prevent misunderstandings, by establishing definitions 
of terms and by calling for adequate information to accompany re- 
ports of tests, so that the reader may know when certain figures are 
not directly comparable. Hence, two important parts of the stand- 
ards toward which we are working are definitions of terms and stipu- 
lations about reporting results. 

Although, to the listener, distortion is anything which makes the 
sounds reaching his ears different in quality from those produced 
by the original source, the present work is limited to the quality 
changes which are caused by the operations of recording and playing 
back or, in other words, the differences between direct and transcribed 
sound. 

The principal topics so far discussed are : 

1. Flutter or wow. 

2. Frequency-response characteristics. 

3. Distortions of the type which cause changes in wave shape. 

4. Noise and signal-to-noise ratio. 



STANDARDS FOR FLUTTER MEASUREMENT 

The Sound Committee of the SMPE, under the able chairmanshipj 
of J. G. Frayne, worked out a series of standards proposals with 
respect to "flutter" or "wow," and these were published in the 
JOURNAL for August, 1947. A great deal of thought and work had 
gone into these proposals, and comments by many individuals repre- 
sentative of different organizations had been invited and considered. 

There was thus available to our ASA subcommittee a draft ofl 
specifications dealing with this important problem, which could weal 
be made the basis of the ASA specification, provided they were like-j 
wise acceptable to makers and users of sound-recording equipment in 
other fields, especially equipment for use with disk records. Broad-j 
cast stations and disk-record manufacturers are represented on our! 
subcommittee and opinions have been invited from others. We be-j 
lieve that the proposals submitted by your Sound committee will 



1948 DISTORTION MEASUREMENT 453 

find general acceptance by all groups interested in sound recording 
perhaps with some additions and changes of wording, but with no 
essential changes of meanings. 

On one item, however, our subcommittee took the position at the 
February, 1948, meeting, that recommendation as an ASA standard 
would be premature, namely, the quantitative part of the definition 
of the term "Flutter Index." While it is admitted by all that the 
information given in the formulation is interesting and valuable, 
several of our members questioned whether it is directly applicable 
to recorded sound in general, the perception threshold for continuous 
tones in a live room being much lower than for ordinary music under 
average listening conditions. In view of the divergent viewpoints, 
recommendation of a standard for Flutter Index may be delayed as 
compared with the remainder of the flutter standards, but it is not 
our intention to postpone action any longer than is needed to arrive 
at an all-around understanding. 

Although none of the subcommittee members has objected to 
specifying flutter in terms of root-mean-square magnitude, a number 
of people have expressed the idea that the peak values of flutter are 
more significant with respect to quality damage than the root-mean- 
square values. The chairman of this committee wishes to take ad- 
vantage of this opportunity to present his personal discussion of this 
and one or two other questions. For better continuity of the report 
of the ASA work, this discussion is put in an Appendix. 

PARAGRAPH NUMBERING 

In what follows, the paragraphs which are numbered, as 3.1, 3.2, 
etc., and the "Notes" directly under them, are the proposed definitions 
or specifications, and notes of explanation which would, if approved, 
'be incorporated in the standards with substantially their present 
wording. Paragraphs not numbered in this manner, or in other words 
the remainder of this paper, are the writer's explanations or discus- 
sions, which have not been put into the form of standards. The num- 
bering employed is part of a topical system, and is of no concern to 
the reader except as he may find some cross references. 

FREQUENCY-RESPONSE CHARACTERISTIC 

It has seemed to the chairman unnecessary to go into details of 
measuring methods for this determination, since the main requirements 
&re rather obvious. However, if any are of the opinion that mate- 
rial should be added to what is here suggested, it is hoped that we 



454 DISTORTION MEASUREMENT November 

shall hear from them. A definition is in order, and the requirements 
to avoid errors due to measuring harmonics or noise instead of the 
true useful output, and it is necessary to specify something about the 
levels at which the tests are to be run. 

3.1 Definition Frequency-Response Characteristic. 

The frequency-response characteristic (sometimes shortened to "fre- 
quency characteristic") of a sound system, or any portion of a sound 
system, is the output level (or "response") as a function of frequency 
for constant sine-wave input, the output being usually expressed 
relative to some arbitrary level, for example, the level at 1000 cycles. 

3.2 All distortion components (harmonics or noise) must be 
excluded from the output measurement. 

3.3 The input level chosen shall be high enough so that at no 
frequency within the range covered is the true output less than 10 
decibels above noise, and low enough so that at no frequency, within 
the range covered, will overloading occur in sufficient degree to af- 
fect the reading appreciably. 

3.3a Another way of stating the second requirement is that the 
input level must be sufficiently below that which would cause over- 
load, so that a characteristic taken at a slightly (say 2 db) lower level 
will, if plotted on a decibel scale, have identical shape. 

3.4 It is permissible, provided the above conditions are met, to 
take part of the measurements with a different input level than the 
remainder. This may be advantageous in testing systems in which a 
large amount of pre-emphasis of high frequencies is employed. 

3.5 The output-input relationship shall be that which occurs 
under steady-state conditions. Thus, if the practice is followed 
of employing a continuously variable input frequency and changing 
this rapidly, the rate of sweep shall be slow enough to give results 
identical with those obtained with a slower sweep. 

NOTE 1 : It is customary to express input and output levels in 
amplitude terms (not power) or else in decibels above or below a I 
chosen reference. 

NOTE 2: The frequency-response characteristic may include in- 
tentional departures from uniformity as, for example, a rising re-| 
cording characteristic by way of pre-emphasis of high frequencies. 

FREQUENCY CHARACTERISTIC OF A RECORD 

For testing the characteristics of reproducing systems, it is necessary: 
to employ test records whose characteristics can be definitely 



1948 DISTORTION MEASUREMENT 455 

specified. It is not always possible to make a logical distinction be- 
tween the losses or distortions which are to be attributed to the record 
and those which should be charged against the reproducing system. 
Whenever it is possible to state the characteristics of the record with- 
out specifying anything about the reproducing system, this is desir- 
able. Hence, it is proposed that 

3.6 The recorded level on a disk record is the velocity (maximum 
of cycle) corresponding to the slope of the centerline of the groove. 

Or, as an alternative definition, 

3.6a The recorded level on a disk record is 2irfa, in which / is 
the frequency and a is the amplitude of the recorded wave. 

NOTE 1 : In the case of records cut in wax and properly processed, 
the velocity of the recording stylus is the recorded level. In the case 
of a lacquer disk, recorded with a cutter having a burnishing surface, 
there is some springback in the record material, and the cutting 
stylus velocity is not a safe guide to the recorded level. 

The amplitude of the recorded waves can be measured microscopi- 
cally. The light pattern method of checking a record calibration is 
believed to be, when carefully carried out, a reliable indication of the 
recorded level. 

3.7 The recorded level on a film is the amplitude of the fundamen- 
tal (sine- wave) component of the sound-track transmission. 

NOTE 1 : A photographic record may be calibrated by measuring 
the reproduced level, using a reproducing system whose performance 
and characteristics are known. The scanning beam should form on 
the film a rectangular image of uniform intensity, having a length 
equal to the standard for the type of track under test and a height 
which is small in comparison with the wavelength, and not more than 
10 per cent of the total light should fall outside the boundaries of the 
rectangle. Correction is then made for the finite width of the scan- 
ning image, by multiplying the output by x/sin x where x = Trw/2\, 
w being the width (or height) of the scanning image and X the length 
of the recorded waves. It is recommended that this correction be 
made small by making w as small as will afford adequate light and 
satisfactory stray-light ratio. 

Specification of recorded level in terms of the cyclic peak is, to the 
best of the writer's information, more widely current than the use of 
root-mean-square figures. The probable reason is that it is more 
simply related to the overload point. The fact that electrical levels 
are specified in root-mean-square terms might be thought to lead to 



456 DISTORTION MEASUREMENT November 

possible confusion, but that danger is lessened by the fact that the re- 
corded level is not an electrical quantity. However, statements of 
recorder or reproducer response must be so worded as to avoid possible 
misunderstanding. 

3.8 In the case of a magnetic recording no way of specifying re- 
corded level seems feasible at present, except as the record is tested 
with a specified reproducing system. 

WAVE-SHAPE DISTORTION 

Since the problem of measuring distortion in recording and re- 
producing systems is in general the same as in any audio transmission 
system (for example, in an amplifier), existing standards are appli- 
cable. Test systems tend to crystallize around developed and avail- 
able equipment. Four types of distortion-measuring equipment have 
found wide use. 

(1) Wave Analyzers, by which the amplitude of each overtone or 
harmonic, relative to the fundamental, can be measured, 

(2) Distortion-Factor Meters, which suppress the fundamental 
and measure the sum total of what is left (overtones, rumble, hum, 
and surface noise), expressing the root-mean-square magnitude of 
this residue, relative to that of the fundamental. At the higher 
levels, and with reasonable control of rumble and hum, distortion- 
factor meters serve to measure total harmonic distortion. 

(3) Intermodulation Analyzers, which measure the fluctuations in 
level of a low-amplitude, relatively high-frequency tone when super- 
imposed on a high-level, low-frequency tone. Levels 20 and 80 per 
cent, respectively, of normal full sound-track amplitude have been 
widely employed. Intermodulation is a more sensitive test (higher 
readings for the same distortion) than total harmonic distortion. 
It has been especially useful in variable-density photographic record- 
ing, and has been employed in a limited way in studying distortion 
in disk recording systems. Equipment now in use gives the choice of | 
several frequencies for the low- and high-frequency components. 

(4) Cross-Modulation Analyzers A high-frequency tone modu- 
lated at a relatively low frequency is recorded. The high-frequency \ 
tone is suppressed in reproduction, and only the output (if any) at the 
modulation frequency is measured. This is essentially a test for rec- 
tification. It has been especially useful in variable-area photographic 
recording. 

There does not appear to be any serious danger of confusion or j 



1948 DISTORTION MEASUREMENT 457 

misunderstanding of the results of the test methods listed above, pro- 
vided the practice is followed of stating the results as " total harmonic 
distortion," "intermodulation distortion," and so forth. Hence, 
our committee may not be called upon to recommend any modifica- 
tion or amplification of existing standards. It is altogether likely 
that in the application of intermodulation testing to disk recording 
(and perhaps to magnetic recording) results may prove to be more 
informative when other frequencies are employed than those adopted 
for variable-density sound tracks. Thus, it would be inadvisable to 
recommend present standardization of frequencies. However, it is 
desirable that intermodulation measurement figures be accompanied 
by statements of the component frequencies. 

Up to the present, trouble has been experienced in making wave- 
analyzer measurements of reproduced tones, because in the available 
meters the filters are so sharp that speed imperfections in the recording 
or reproducing machines have prevented the proper functioning of the 
wave analyzer. We understand that instruments with broader 
filters will, in the near future, be available. The same problem can 
occur in distortion-factor meters, but several models have been on 
the market which have been entirely satisfactory in this respect. 

NOISE AND SlGNAL-TO-NoiSE RATIO 

In the measurement of noise there has been considerable variation 
of practice, and still more divergent practices are followed in specify- 
ing the signal level with reference to which the noise is to be stated. 
In some cases the noise is measured with a "flat" reproducing system, 
and in others with a reproducing system which has purposely been 
given a drooping characteristic to lessen the noise. Filters to elimi- 
nate hum and rumble are sometimes employed, especially when the 
purpose is purely a study of record materials. In stating signal level 
it has been customary in the film industry to use practically the maxi- 
mum permissible recording level. The same practice will probably 
be followed in magnetic recording. On the other hand, in the field of 
mechanical or disk recording it has long been customary to employ a 
reference level or 1000-cycle standard signal which on a volume indi- 
cator gives a reading that safely may be equaled when recording regu- 
lar program material. In this there is an allowance of about 10 
decibels for peaks. The standard reference signal generally adopted 
is t\vo inches or five centimeters per second, maximum velocity. The 
recordist notes the reading on his volume indicator produced by the 



458 DISTORTION MEASUREMENT November 

standard signal, and then knows that if he does not let his volume in- 
dicator (which is somewhat sluggish) go above that reading, he is rea- 
sonably safe with respect to the sudden peaks. Such a reference 
signal has unquestioned utility, but it does not have to be identical 
with the reference for specifying the signal-to-noise ratio of which a given 
recording system is capable. The difference in practice may readily 
lead one not familiar with the situation to think that a mechanical 
system is about 10 decibels worse than it is actually is, in comparison 
with other systems. 

Fully conscious of the difficulties of inducing groups of people to 
change any of their practices, we have nevertheless thought it worth 
while to raise the question whether unified practice and terminology 
are attainable and, in order that those who are interested may judge 
better what might be involved, an attempt has been made to draw up 
some specific proposals which, it is hoped, might be acceptable as not 
upsetting established practices, while reducing the likelihood of mis- 
interpretations When it is not feasible to have all people follow 
identical procedures, it should at least help prevent misunderstand- 
ings if certain information is given when reporting results, a require- 
ment to which scarcely anyone could object In the first place, it is 
proposed that the present 5-centimeter-per-second tone be called the 
"recording reference signal," and that another signal, to be called 
"maximum signal," be employed for determining the signal-to-noise 
ratio of a system. Since the recording reference signal would not be 
directly employed in signal-to-noise determinations, its definition 
does not belong in the present specification, but a note is included to 
point out the distinction. 

Proposed definitions and specifications for signal-to-noise deter- 
minations are as follows : 

5.1 Noise The term noise, as applied to a sound-reproducing 
system, means any output power which is not of the same frequency 
as the input, except that distortion products (harmonics or rectifica- 
tion terms ) are not usually regarded technically as noise. 

NOTE 1: Noise is commonly comprised of hum, rumble, or the 
effect of mechanical vibrations, microphonics, thermal noise (in low- 
level input circuits), tube noise, phototube hiss, and, in recorded 
sound, surface noise in the case of mechanical records or graininess 
plus scratches and dirt in photographic records. 

Noises such as thermal noise, phototube hiss, record surface noise, 
and graininess in film sound tracks have an energy distribution such 



1948 DISTORTION MEASUREMENT 459 

that the power within any frequency band is approximately propor- 
tional to the width of the band in cycles. 

NOTE 2: The usual method of measuring noise in any type of 
sound record, is to reproduce from an unmodulated record and meas- 
ure the noise in the reproducing system. 

5.2 Modulation Noise The presence in a record of the factor 
which produces output (light transmission in a film, slope of a groove, 
or a magnetization in a wire or tape) results in an increase in noise as 
compared with the condition of no modulation. This extra noise, 
which is modulated with the signal (generally at double signal fre- 
quency) is called "modulation noise." The increase in noise due to 
removal of ground-noise reduction bias in photographic sound tracks 
is not true modulation noise. 

NOTE 1 : Modulation noise may be measured by recording a tone 
(usually of relatively low frequency) and measuring the reproduced 
output with the recorded tone eliminated by a band-suppression fil- 
ter of sufficient bandwidth effectively to eliminate the recorded tone. 

5.3 The frequency characteristic of the reproducing system used 
for measuring noise in recorded sound should be the same as that of the 
reproducing systems with which the record is designed to be used, 
except that if the reproducing systems include compensation for loud- 
speaker characteristics, such compensation should be omitted for the 
measurement. 

5.4 A statement of the frequency range covered by the repro- 
ducing system used in a noise measurement should accompany a 
report of the measurement. If the frequency characteristic is ap- 
proximately flat between the droops at the ends, the range may be 
stated as between the frequencies at which the response has dropped 6 
decibels below the average within the effective range. If the re- 
producing characteristic used in the noise measurement is one that 
has been standardized (as in the case of theater systems) reference to 
the standard may serve as description of the reproducing characteristic. 

5.5 If a high-pass filter is used for excluding hum and rumble when 
measuring record noise, this should be stated, and the cutoff point of 
the filter. 

5.60 Maximum Signal Maximum signal is a pure tone of the 
maximum level that can be recorded without overload.* 

* This is to be distinguished from Recording Reference Level employed in mechani- 
cal systems, which has been standardized as 2 inches or 5 centimeters per second 
(maximum velocity of cycle) and is about 10 decibels below maximum signal. 



460 DISTORTION MEASUREMENT November 

5.61 The level of maximum signal is the highest compatible with 
the condition that if the input is varied as specified in 5.62, at no 
frequency will the distortion exceed a specified amount (for example, 
10 per cent intermodulation) . 

The distortion permitted in this determination should be specified 
in reporting the value of maximum signal. 

5.62 In view of the fact that in nearly all program material com- 
ponents of high frequency are rarely present in magnitudes as great 
as the components of lower frequency, it is permissible for establish- 
ing maximum signal level to reduce the input level in the high-fre- 
quency range in accordance with the following rule : the input shall 
be maintained at constant level from the lowest frequency comprised 

n the recording range, up to 1500 cycles, above which the input 
level may be reduced at the rate of 4 decibels per octave. 

NOTE 1 : The purpose of Specification 5.62 is to permit the employ- 
ment of a safe amount of pre-emphasis of high frequencies in record- 
ing. By "safe" is meant that only in exceptional cases will material 
to be recorded have peak high-frequency components with magnitudes 
(relative to the peak magnitudes in the low-frequency range) any 
greater than indicated by the characteristic described in 5.62.* It is 
anticipated that the figure, 4 decibels per octave, and perhaps, also, 
the 1500-cycle transition point, should be reviewed from time to 
time in the light of accumulated experience. It should be recognized 
that this characteristic is to be determined solely by the nature of the 
spectra of music and speech, and that it does not and should not make 
any allowance for properties of recording systems which may cause 
overload to occur at lower levels in one portion of the frequency range 
than in others. It is, however, in order, that this permitted droop 
should take account of distortion tolerance, provided experience justi- 
fies such an allowance. (For example, harmonics of high-frequency 
tones may not be reproduced, and if cross-modulation is not en- 
countered, the tolerance may be greater in this range.) 

5.7 Signal-to-Noise Ratio Signal-to-noise ratio is the ratio of 
maximum signal to noise. 

* Allowable pre-emphasis is discussed in a report by J. K. Hilliard and J. P. 
Maxfield in Audio Engineering for April, 1948. Permissible pre-emphasis has 
been well expressed by Hilliard as "that which causes equal probability of dis- 
tortion at any part of the important frequency range covered by the record." 
It is also pointed out that compensation for reduced response of some element of 
the recording channel (such as high-frequency droop of a microphone) is not a 
part of pre-emphasis. 



1948 DISTORTION MEASUREMENT 461 

5.71 The limiting distortion (as, for example, 2 per cent total 
harmonic distortion or 8 per cent intermodulation distortion) per- 
mitted for the purpose of determining maximum signal should be 
stated when reporting signal-to-noise ratio, and also the information 
with respect to the noise measurements, called for in 5.4 and 5.5. 

NOTE 1 : It is evident that a high-quality system which sets a low 
limit to permissible distortion, and which reproduces a wide fre- 
quency range, cannot realize from a given record material or surface 
quality, as large a signal-to-noise ratio as a system in which more dis- 
tortion is permitted and a limited frequency range covered. 

APPENDIX 

(Discussion of some of the proposals on which there have been differ- 
ences of opinion.) 

SPECIFICATION OF FLUTTER IN TERMS OF ROOT-MEAN-SQUARE 

Although the proposal to define flutter as the root-mean-square 
deviation in frequency has had the approval of both the SMPE sound 
committee and the ASA subcommittee, a number of engineers have 
expressed the belief that the peak deviation is likely to be a better 
measure of the quality damage than either the root-mean-square or 
average deviation. I believe that the thought behind this view is 
that we tolerate small fluctuations in speed and may be quite un- 
aware of them, but the larger deviations from average speed are 
quickly noticed ; therefore, it is reasonable to suppose that maximum 
deviations are what count. This reasoning is quite logical, but when 
comparing a peak-reading meter with a root-mean-square meter, the 
question is not whether extra importance should be attached to the 
largest deviations, but whether everything else should be ignored 
and no consideration given to the duration of the large deviation. 
Fig. 1 shows several types of flutter curve, all having the same peak 
value. In curve B, there is little beside the one high peak, while 
curve A shows numerous other fluctuations of only slightly lower 
amplitude than the peak, and curve C shows deviations which last 
many times longer. Should these three be rated alike? 

Someone comparing these curves may bring up the point that if the 
flutter-measuring system is provided with a weighting network such 
as the "Flutter-Index" idea suggests, thus emphasizing flutter of 
rather slow rates, the peak-reading meter would give much larger 
readings for the flutter shown by curve C than curve J5, since the 



462 



DISTORTION MEASUREMENT 



November 




short sharp peak of B could be produced only by high-frequency com- 
ponents. The reply to this is that if and when such networks come 
into general use, there will be much less difference in the actions of 
peak, root-mean-square, and average-reading meters. Such a net- 
work narrows the band of nut- 
ter rates to which full weight 
is given (with attenuation on 
both sides of the range 1 to 5 
cycles). Were only a single 
nutter rate to be considered in 
any one measurement, it would 
make no difference which type 
of meter is used, for their indi- 
cations would be in fixed ratio, 
and agreement in readings is 
only a matter of calibration or 
scale. (A pure sine wave with 
a peak value of unity has a 
root-mean-square value of 
0.707 and an average value of 
0.64.) But grave errors would 
result from assuming that these 



V 




Fig. 1 Three frequency-deviation 
curves for which a peak-reading meter 
would give the same reading. 



ratios Avould hold for the ragged waves shown by ordinary flutter 
records. 

The characteristic of a root-mean-square meter is admirably adapted 
to giving special weight to the larger frequency deviations. A 1 per 
cent deviation of given duration has four times the effect on the meter 
that a 0.5 per cent deviation of the same duration would have. Why 
then does it not read four times as high? The answer is that, in 
general, the effect which deflects the needle does go up as the aver- 
age square of the quantity being measured, but the meter is provided 
with a nonuniform scale which in effect extracts the square root. 

There is reason for believing that the square law r is a fairly good 
approximation to the noticeability of flutter of any given rate. At 
least we can say this, there is a threshold magnitude below which no 
one notices the flutter, but with small increases, it seems to get 
bad very rapidly, and the number of people who notice it increases 
rapidly. For example, in a letter on the subject, Kenneth Lambert 
wrote "We have observed here that 24-cycle flutter may become 
rapidly objectionable with an increase from perhaps 0.1 to 0.13 per 



1948 DISTORTION MEASUREMENT 463 

cent (on a root-mean-square basis) and 96-cycle flutter in much the 
same degree." If you were to attempt to draw a curve which would 
represent the harmful effect of flutter as affected by its magnitude, 
you would draw something that looks a good deal like a parabola. 
But what about a meter of the rectifier type, which reads the 
average of the waves? I think I can give an illustration of a case in 
which such a meter would be decidedly in error. Suppose you were 
comparing two machines, one of which produced every second a 
1 per cent deviation that lasted a tenth of a second, while the other 
produced every second two deviations of 0.5 per cent each lasting a 
tenth of a second. The root-mean-square meter would rate the for- 
i mer as twice as bad. The averaging meter would say they were equal. 
You will notice that the flutter specifications as they now stand, al- 
though stating the standard as a root-mean-square reading, sanction 
| the use of meters of the rectifier type. Meters of this type actually 
t show something between the root-mean-square and average values 
j of the waves, and therefore it is believed that the difference ordinarily 
will be small. In view of that consideration, and the fact that 
! equipment is in wide use having various types of indicating instru- 
ments, it has not appeared practical to call for strict adherence to the 
root-mean-square standard, but it is an urgent requirement that the 
type of measurement be clearly stated when a measurement is reported. 
Examination of a flutter oscillogram (or "wowgram") does not enable 
' one to arrive at a root-mean-square figure, hence the widespread prac- 
f tice on the part of those who have recording meters, of reporting flutter 
L as the peak-to-peak value. It is hoped that future recording meters 
will also be equipped with root-mean-square indicating meters, so 
that simultaneous readings may be taken. Meantime it is important, 
in order to avoid confusion, that statements of flutter magnitude, 
based on inspection of a wowgram, should be accompanied by enough 
information to make clear how the wowgram was read, such as 
"peak deviation from average," or "range positive to negative peak," 
iand to make certain that the figure will not be taken as a root-mean- 
square measure. 

FLUTTER INDEX 

The subject of "Flutter Index" as proposed by the SMPE sound 
committee has met with many questions and indications of doubt. 
Not that many doubt the correctness of the tests for the conditions 
under which they were made, but they doubt the applicability of the 
formula to the actual conditions under which reproduced sound is heard. 



464 DISTORTION MEASUREMENT November 

For what bearing it may have on the questions in people's minds, I 
would like to call attention to a curve published by Shower and Bid- 
dulph in a paper on "Differential pitch sensitivity of the ear," in the 
Journal of the Acoustical Society of America, October, 1931. Their 
curve showed the threshold of perception of rhythmic frequency 
changes of a 1000-cycle tone at rates from 0.7 to 5.5 cycles per second, 
the listening being done with headphones. The interesting thing is 
that this curve, although having a minimum some 10 times higher 
than the minimum for a 1000-cycle tone as found in the live-room 
listening tests, was very nearly the same shape. 

If nutter rate affects perception threshold in the same manner under 
the two extreme conditions of complete absence of reverberation on 
the one hand (headphones) and live-room listening on the other, the 
general shape is probably not far off for intermediate conditions. 

Thus, although the evidence is still insufficient ( the Shower and the 
Biddulph data should be supplemented with tests at higher nutter 
rates, and with other tones, and tests also made in moderately damped 
rooms) , there is a presumption that a curve of the general shape in- 
dicated by the Flutter-Index formula would, to a fair degree of ap- 
proximation, express the relative perceptibility of nutter under aver- 
age listening conditions. 

Ultimately, it is hoped, such a formula and weighting factor can be 
"proved in" for music. Recent experience has demonstrated to the 
writer's own satisfaction, that the tolerance for rapid nutter is much 
higher than for slow nutter. Thus, so far as this small item of in- 
formation goes, it points to a similar relation for music as for steady 
tones, although again probably with a higher threshold throughout 
than for steady tones. 

RATE OF REDUCTION OF INPUT OF HIGH FREQUENCIES 

In many systems of recording, the practice has been followed of 
increasing the amplification in the recording channel with increasing 
frequency. This has been called "pre-emphasis." In order that the 
final sound shall not have exaggerated high frequencies, the reproduc- 
ing system is given a drooping characteristic and this has been called 
"postequalization." The result is a desired over-all frequency char- 
acteristic, but a large reduction in surface noise or in graininess noise 
due to the imperfections of the record. Pre-emphasis is possible 
without excessive overloading at high frequencies, for the reason that 







DISTORTION MEASUREMENT 



465 



except in rare instances the program material itself contains the high 
frequencies, only in very much reduced amplitudes. There are two 
possible ways of ascertaining how much pre-emphasis is safe or in 
other words how much may be employed without resulting in any 
more overloading at high frequency than in the lower range. The 
first method is to make extensive measurements such as those re- 
ported by Sivian, Dunn, and White (Journal of Acoustical Society, 
April, 1931) and by Dunn- and White in the January, 1940, issue of 
that Journal. 




Fig. 2 Input droop for determination of maximum signal. 
I. Orthacoustic-recording characteristic. II. Assumed safe pre-emphasis. 
III. Permissible high-frequency reduction. 

The other method is one of cut-and-try, namely, to make record- 
ings with various amounts of pre-emphasis or " tip-up," and learn 
from general experience how much may be used. Because of the very 
extensive use that has been made of the "orthacoustic" recording 
characteristic (see Fig. 2), this appears to be the best general guide 
to possible tip-up. I have endeavored to obtain expressions from 
engineers who have had experience with this system, and while some 
express the opinion that the tip-up is excessive there does not seem to 
be any overwhelming evidence to that effect. The overloading at 
high frequency seems to be rather because of the fact that in disk 
recording the actual overload level (in terms of velocity) is lower at 
high frequency because of curvature effects, especially near the 



466 DISTORTION MEASUREMENT November 

inside of the records. If the overload point were always at the same 
velocity the orthacoustic rate of tip-up probably would not be exces- 
sive, or in other words, it does not more than offset the droop in input 
as found in a variety of programs. Following this line of reasoning 
the writer suggested to the members of our ASA subcommittee that 
we propose, for testing purposes, holding the input constant to 1500 
cycles and then dropping at the rate of 5 decibels per octave. This 
would be slightly less than the complement of the orthacoustie- 
recording characteristic. However, some of the committee thought 
we should be more conservative, suggesting 3 instead of 5 decibels 
par octave above 1500 cycles. For purposes of discussion I have 
called, in the present draft, for 4 decibels per octave. I hope to re- 
ceive more expressions in regard to this question. The pre-emphasis 
used in film recording is too small to constitute a test of this factor. 

If a recording system is designed with a large amount of pre- 
emphasis it may in practice be quite capable of handling high levels 
of recording, but if tested by means of an oscillator with constant- 
voltage input throughout the frequency range, obviously it would be 
badly overloaded at the high-frequency end, unless the input through- 
out the entire range were dropped to a level far below the power- 
handling capacity of the system. We therefore think it justified to 
suggest that the determination of maximum signal (especially for 
signal-to-noise determinations) be made with an input which droops 
at high frequency, as shown, for example, by curve /// of Fig. 2. 

If the actual overload level of the system is the same at all fre- 
quencies (as, for example, in a variable-area recording) a tip-up of 4 
decibels per octave above 1500 cycles could, if curve /// is what it 
should be, be employed without any greater likelihood of overload at 
high frequency than at low. 

If a system overloads at a lower level in a certain frequency range 
than in another, then either the over-all level will have to be dropped 
in order to meet the specifications for determining maximum signal, 
or else the recording characteristic should be modified to reduce the 
recording level in this critical range. For example, assuming 4 
decibels per octave above 1500 cycles to be the maximum safe pre- 
emphasis with constant overload level, disk-recording systems would, 
on account of the curvature troubles, either have to establish their 
"maximum signal" somewhat below the level which constitutes 
overload in the low- and middle-frequency range, or else stop short of 
applying the 4 decibels per octave all the way up to 12,000 cycles. 



1948 DISTORTION MEASUREMENT 467 

DISCUSSION 

J. P. MAXFIELD: In connection with the matter of this equalization, I had the 
opportunity to obtain simultaneous cuts of records running 15 decibels at 10,000, 
around nine and around six. Those were all played with the standard droop for 
the higher present equalization. Astonishingly enough, the one with the 6- 
decibel rise in the recording reproduced, more highs and cleaner highs than the 
one with the 15, indicating that the overload on the latter was so bad that it 
was not being tracked. Unfortunately we have only some three sets of such rec- 
ords, but I think the situation should be carefully looked into before we pick as 
high a rise as 15 decibels to 10,000. 

J. K. HILLIARD: I should like to make some comment along this line, in support 
of Mr. MaxfiekTs statement. There is other information that also verifies that we 
should be cautious in the matter of equalization. I think the experience of the 
studios in having parallel disk and film channels would indicate that if equaliza- 
tion is provided higher than the six or eight or possibly even ten at a maximum, we 
get into this bootstrap lift, the effect of having to lower the level or use excessive 
limiting at times and since present equalization is used primarily to increase the 
signal-to-noise ratio, if we have to lower the level on the disk or the film in a 
general case, then we are defeating the purpose we went out to obtain, and we 
have the two problems of having to lower the signal on the record at the time if 
we used higher amounts of equalization, and the effect that Mr. Maxfield talked 
about, improper tracking, leads to inferior results over that used with lower 
amounts of equalization. 

CHAIRMAN C. R. DAILY: There is another point, that of excessive modulation 
at high frequency. Most types of recording systems lead to increase of cross- 
modulation production which may do more harm than the increase in signal level. 

E. W. KELLOGG (by letter) : The experiences recounted by Mr. Maxfield and 
Mr. Hilliard are just the kind of evidence which we are seeking, and I hope more 
experiences bearing on this subject will be reported. The suggested 4 decibels 
per octave above 1500 cycles gives a level difference between 1000 and 10,000 cycles 
of about 11 decibels which is 4 decibels less than that given by the orthacoustic 
curve, and much nearer the conservative figure which I think Maxfield and Hilliard 
would approve. But please notice that to say that the input may be drooped at 
a certain rate for test purposes, is not by any means equivalent to recommending 
a tip-up of equal amount. Our purpose is to try to arrive at a curve which repre- 
sents the droop which may be expected to occur in average program material. 
If, as in disk recording, overload tends to occur at lower levels in the high-frequency 
range (due to curvature) it obviously would be inviting overload, to use a tip-up 
which completely offset the normal droop. Hence the figure suggested here may 
not be out of line at all with the observations just reported. The question then 
arises, how have the people who have used the orthacoustic- recording characteris- 
tic gotten by with it as well as they have? There are, of course, differences in 
microphones, but, more important, the recordist can exercise a wide control by 
such factors as orchestra arrangement, microphone placement, and room acous- 
tics. The influence of these factors makes it impossible to say what the average 
or normal droop is, but some more or less arbitrary specification seems to be 
needed for putting testing systems on a common basis, and unless experience 
indicates clearly that it should be revised (and it is open to revision), the figure 
proposed in the paper seems to me to be reasonable. 



Magnetic Recording 
for the Technician* 

BY DOROTHY O'DEA 

FORMERLY, RCA VICTOR DIVISION, HOLLYWOOD, CALIFORNIA 



Summary The first half of this paper will present to the motion picture 
technician a review of magnetic-recording theory; the second half consists 
of experimental data taken with the new magnetic-recording equipment of 
the Radio Corporation of America. Input-output, frequency-response, and 
distortion data, which were taken under test conditions familiar to motion 
picture technicians, are presented. There are many excellent articles 
available which treat the various aspects of this subject. Those who are 
interested in the detailed scientific explanations are referred to these articles, 
listed in the bibliography, and to the extensive patent literature. This 
paper attempts to consolidate the information in these articles in simplified 
form and to provide a useful picture of the phenomena in magnetic record- 
ing and reproduction for those whose primary interest is in the application of 
the theory. 

PART I THEORY 

PERHAPS A GOOD starting place for a discussion of magnetic re 
cording would be the two distinct types of magnetic material 
which are essential parts of the system. Materials are classed in thi 
groups from a standpoint of magnetism. A vacuum has a perm< 
ability of unity, which means that the ratio of magnetic induction 
to magnetizing force H is 1.0. Diamagnetic materials have a perni( 
ability less than unity. Paramagnetic materials have a permeability 
somewhat greater than unity. The ferromagnetic materials have 
permeability very much higher than unity and this permeability 
is variable depending on the particular material and the magnetizii 
force applied to it. We are concerned only with these ferromagnetii 
materials. They can be subdivided further into two types; hai 
and soft, both of which are used in magnetic recording. Soft rm 
netic materials, which incidentally are usually soft physically, have 
low retentivity; that is, they are easily affected by a magnetic fielc 
and easily lose the effect when the exciting field is removed. This 
type of material is commonly used in transformers, galvanomet 
pole pieces, and magnetic heads. 

* Presented May 18, 1948, at the SMPE Convention in Santa Monica. 
468 NOVEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 



MAGNETIC RECORDING 



469 



The other type of magnetic material, which is called hard, has high 
retentivity; that is, it is not so easily affected by a magnetic field 
as the soft materials, but when affected, has the property of retaining 
a major portion of this effect after the exciting field is removed. An 
example of this is the familiar permanent magnet. Now it is ob- 
vious that if a long strip of this hard material were to be subjected to 
a magnetic field which was varying according to a voice signal, while 
the material was moving at a constant rate, a sound record would be 
impressed on the material. In order to confine the signal to a reason- 
able length or a reasonable speed for a given length, it is desirable to 




PERPENDICULAR 



TRANSVERSE 

Fig. 1 Types of recording longitudinal, perpendicular, transverse. 

limit the exposing effect at a given instant to a small portion of the 
hard magnetic material. This is, of course, obvious, as in photo- 
graphic recording. 

The difficulties of confining the signal to a small portion when 
using a coil as the exciting field are apparent. Therefore, the coil is 
wound around a core which also increases its efficiency considerably. 
This core contains an air gap so that the magnetic lines of flux going 
around the core leak out at the gap. The hard material is pulled 
over the top of the gap, thereby recording and retaining the leakage 
flux which varies according to the audio signal. There are various 
methods of placing the film in the region of influence of the core or 
magnetic head, as shown in Fig. 1. With the perpendicular method, 



470 O'DEA November 

the film is actually passed between two pole pieces or is pulled through 
the gap. Here the length of the magnet from north to south is con- 
stant for a given film thickness. One advantage of this method is 
that the aspect ratio of the individual wavelengths, which make up 
the signal, is less effective in controlling the high-frequency response. 
One disadvantage of this method is that it is desirable for reasons of 
efficiency and quality to have the gap as narrow as possible, thereby 
necessitating a very thin film which then introduces the problem of 
strength and durability of the film. 

The next method, shown in the right-hand corner, transverse 
recording, has the same advantage as the perpendicular method of 
constant-aspect ratio, but has the disadvantage of using a narrow 
tape. Here the length of the magnets from north to south is constant 
for a given film width. Very little information has been found in 
the literature on this type. There seems to be no practical use for it 
in tape recording and in wire recording it is the same as the perpen- 
dicular method. 

The method of longitudinal recording is more commonly used at 
the present time. It is the method which RCA is using and will be 
discussed in more detail. Three types are shown here. The first 
type uses only one pole piece; the second uses two offset pole pieces; 
and the third method uses the ring-type head. In all three types the 
length of the magnets from north to south depends on the wavelength 
of the signal. It is apparent that with this method, wide, strong film 
can be used, as only the thickness of the coating is important mag- 
netically. Sturdy pole pieces can also be used and the gap width 
can be very small. The principal disadvantage seems to be that the 
aspect ratio decreases with increasing frequency, resulting in high- 
frequency losses. 

Now that we have covered very simply the method of recording, 
let us return to the type of materials used and a brief discussion of 
the properties of materials best suited for this purpose. The most 
desirable magnetic material for the core would be one which has a 
very high initial permeability, very low hysteresis loss, and very 
low eddy-current losses. . 

For commercial purposes, MU metal meets these requirements 
satisfactorily. It is listed as having an initial permeability of 7000, 
hysteresis loss is acceptable, and the eddy-current losses are mini- 
mized satisfactorily by laminating the cores. 

The characteristics of the high-retentivity material used for the 



1948 MAGNETIC RECORDING 471 

film appear somewhat more involved. Any investigation of films is 
very complicated unless certain factors are kept constant such as tape 
speed, thickness of emulsion layer, and construction details of the 
heads. The obvious starting place for an investigation of films would 
be a study of the hysteresis loop of the iron-oxide material. However, 
there seems to be considerable controversy about the value of these 
curves for magnetic recording. It seems reasonable to doubt that 
the theory of magnetic recording could be traced out directly on this 
curve, if only because of the secondary effects introduced by the bias 
frequency (which will be discussed later) . We believe that it will be 
essential to find some modification of this curve with which we can 
correlate practical experiments with theory. Several investigations 
are being carried out along these lines, but to date, we know of no 
theory which successfully explains all the factors involved in record- 
ing. The following hypothesis is presented with knowledge of the 
many deficiencies it contains. It is hoped it will provide a useful 
picture and a stimulus for more comprehensive work. The stand- 
ards book 1 of the American Society of Testing Materials has been 
use as a reference for the definitions of magnetic terms. 

Fig. 2 shows in a highly simplified manner the over-all transfer 
characteristics of magnetic recording and reproduction. This figure 
does not show any of the phenomena peculiar to the type of film, fre- 
quency, or speed of recording, but some of these factors will be taken 
up as individual steps. 

Starting with the audio current, shown in the lower left corner, 
which is combined with a high-frequency biasing current, the currents 
produce magnetic flux by the action of the coil. The flux which then 
flows in the core and across the gap is proportional to the current if 
the core material has low losses and has a saturation value above the 
range required. For our purpose, we can assume that the head has a 
straight-line transfer characteristic, and the 45-degree line in the 
lower left corner represents this characteristic. The signal on the 
left represents the flux in the core. The magnetic flux across the 
gap causes a magnetic force to affect the film which is passing over 
the gap and this force results in the magnetic flux flowing into the 
film. The line in the upper left corner represents the film characteris- 
tic which is nonlinear. It is effectively straightened out by the 
biasing current. As the film is a permanent magnet and is being 
moved past the gap, this flux leaves the film in a magnetized condi- 
tion. Now the film is a magnetized body and is effectively the same 



472 



O'DEA 



November 



as the record head in that its force will produce a magnetic flux in t 
air surrounding it. It differs from the record head in that its for 
is permanent and varies with distance along the film while the force 
in the record head varies with time. The curves at the top show the 
forces on the film and the dashed line shows the resultant force. 

The film is now ready for immediate reproduction if desired. When 
it is passed over another head the flux in the air around the film passes 
into the head and induces in the coil an electromotive force which is 
amplified in the customary manner. The line in the upper right 



s 




INPUT TO RECORDING HEAD INPUT TO REPRODUCING AMPLIFIERS 

Fig. 2 Over-all transfer characteristics. 

corner represents the transfer from flux around film to flux in the 
head. The line in the lower right corner represents the transfer 
from flux in the head to induced voltage. 

Fig. 3 shows a way in which the recording action can be represented 
simply although it does not show some important effects. For the 
purpose of illustration, the input signal in the lower left corner is 
drawn as if it were a 9000-cycle audio wave with 27 kilocycles bias. 
The numbers indicate representative points on the signal which can 
be found on the magnetization curve. The arrows on the magnet- 
ization curve show the travel of the biasing action. The waves on 






1948 



MAGNETIC RECORDING 



473 



the right indicate the magnetization on the film and the numbers 
represent the same points as on the original input wave. The re- 
sultant signal is formed by these two waves and is seen to be an un- 
distorted signal. Directly above the biased input signal is an un- 
biased input wave and it is apparent that the jog in the magnetization 
curve will cause the output wave to be distorted as shown on the 
right. The bias current keeps the audio current above this jog or 
effectively straightens out the curve. If insufficient bias is used, 
distortion results and the output level drops. If too much bias is 
used the output level also drops. 



MAGNETIZATION CURVE 





Fig. 3 Enlarged view of recording characteristic. 

The effect of demagnetization, which was mentioned earlier, oc- 
curs in the recording operation. In longitudinal recording, the 
wavelength is recorded along the length of the film and at 9000 cycles 
the wavelength would be 0.002 inch at normal motion picture film 
speed. The width of the recorded track is 0.200 inch so a half wave 
consists of a rectangular magnet 0.200 inch wide and varying from 
north to south along a length of only 0.001 inch. This ratio is not at 
all to the liking of a magnet and it has a strong tendency to demagnet- 
ize itself. This ratio has been expressed 2 as "aspect ratio" 
and the example given above would have an aspect ratio of 0.005. 



474 



O'DEA 



November 



Manildi 2 has shown that an efficient magnet should have an aspect 
ratio of at least 8 for a certain permanent-magnet material. In order 
to determine with any accuracy the proper aspect ratio for our re- 
cording films, it would be necessary to know the effective hysteresis 
curve of the material. However, it is probable that a ratio of 0.005 
is low enough to cause high-frequency losses comparable to slit losses 
or greater. 

Camras 3 presents an interesting study of this effect on wire re- 
cording and points out that fortunately some of the effect is counter- 




EQUALIZED FILM 



s 




900 1000 

FREQUENCY 



10,000 



Fig. 4 Frequency-response characteristic with and without equalization. 

acted by the action of the reproducing poles. Concerning this coun- 
teraction, Wetzel 4 shows that the present recovery during playback 
increases with increasing frequency, but that the sum of these oppos- 
ing tendencies is a net decrease in output with increased frequency. 
Equalization is provided in recording to compensate for this loss as 
well as slit loss. A third factor which influences the high-frequency 
response is the penetration effect. Kornei 6 also discusses this. 
When the thickness of the recording layer is decreased, the output 
level of the low frequencies drops, while the relative high-frequency 
response improves. The penetration of the magnetization depends 



1948 MAGNETIC RECORDING 475 

on wavelength, permeability, and gap width. However interesting 
this effect may be, there is little need to go into it further at this 
time, because, as Kornei 5 points out, the effect is extremely small with 
thicknesses in the order of 0.0005 or 0.001 inch. The amount of 
equalization required for demagnetization and slit loss is quite small 
compared to that required for the next effect. 

In reproduction, the output voltage theoretically is directly pro- 
portional to frequency for constant-amplitude input. The pickup 
can be considered a generator with the head itself acting as a coil 
which remains stationary in a changing magnetic field. As the flux 
surrounding the film enters the region of the gap, the force causes 
flux to flow in the core of the head and as this changing flux links 
the electrical circuit of the coil, there is induced in the coil a 
voltage which tends to oppose the change. This voltage will be 
out of phase with the flux because when the flux passes through zero, 
the rate of change is maximum and, therefore, the voltage is maxi- 
mum. The voltage is proportional to frequency because in a given 
distance the rate of change for a high frequency is greater than for a 
low frequency. The equalization required to compensate for this 
effect is 6 decibels per octave from whatever frequency is set as the 
low-end limit to the frequency at which demagnetization and slit 
loss take effect. 

Combining these several causes of frequency changes, we have the 
familiar frequency-response characteristic without equalization (Fig. 
4) . As the equalization required for the low end is the larger amount, 
it will affect signal-to-noise ratio. Our experience has been that with 
most good films, the equalization brings the output down to about 
50 decibels above system noise with the film noise below system noise. 
Care must be taken to keep system noise as low as possible. Another 
way to increase signal-to-noise ratio, is to tolerate a higher frequency 
as the lowest limit. For example, if the lowest frequency desired is 
100 cycles, the output and consequently the signal-to-noise ratio is 6 
decibels higher than it would be if the lowest frequency were 50 
cycles. 

PART II EXPERIMENTAL DATA 

All the test data presented here have been taken with RCA's new 
magnetic-recording kits. In the interests of users of these kits, they 
were designed, not to obtain optimum conditions for this type of 
recording, but to obtain the least possible difficulty in the studios 



476 



O'DEA 



November 



caused by changing from photographic to magnetic film. Using an 
existing recorder created many constructional difficulties such as 
space for the heads, plugs, and mounting arrangements. Also, in 
the interests of users, the decision was made early to use 35-mm film 
with standard dimensions and perforations. In the fall of 1946, 
duPont was approached with a request for some experimental film 
on 35-mm base. In February, 1947, the first samples of this film 
were received and tests were started with a Brush head. These first 
tests indicated that the general idea of 35-mm magnetic film was 



+ 16 OBM INPUT 




BIAS CURRENT-MA 



Fig. 5 Bias input versus audio output. 



practical and construction on RCA heads was started by our develop- 
ment-engineering group in Camden. These new heads were then 
mounted on a PB-36 soundhead with some of the same features it 
was intended to incorporate in the final design. During this time, 
other film manufacturers were becoming interested in this field and 
the original maker was constantly improving his samples. It is 
not the intent of this paper to make comparisons between films made 
by different manufacturers. However, it is difficult to avoid dis- 
tinguishing between films, because of the difference in equalization 
required. Complete tests have been made on only duPont and 



1948 MAGNETIC RECORDING 477 

Minnesota Mining films, both of which could be used for recording. 
For the purpose of demonstrating the capabilities of this system, all 
the data in this paper were made on duPont SW4 film. 

BIAS INPUT VERSUS OUTPUT 

A good starting place for film tests appears to be a curve of bias 
input versus audio output (Fig. 5) shown here for two input levels. 
As mentioned earlier, the bias current has the effect of straightening 
the transfer characteristic of the film, thereby decreasing distortion. 




+ 8 +16 

AUDIO INPUT DBM 



Fig. 6 Audio input versus audio output. 

Output is increased with increasing bias current up to a certain point, 
after which output decreases with increasing bias current. Some 
investigators think of this decrease as being caused by the bias current 
being high enough to erase the audio signal. 

AUDIO INPUT VERSUS OUTPUT 

Now that the optimum bias current has been chosen, a curve is 
plotted of audio input versus output (Fig. 6) using this bias current. 
Linearity is very good up to the overload point of the film. This 
overload is gradual, being somewhat similar to the characteristic of 



478 



O'DEA 



November 



I 5 - 



Fig. 7 Audio output versus total harmonic distortion. 



TPUT{+ I60BM INPUT) 




STORTION(-H6D8M INPUT) 



DISTORTION (+4 OBM INPUT) 



23 4 5 6 

BIAS CURRENT-MA 



9 10 



Fig. 8 Bias input versus total harmonic distortion. 



1948 



MAGNETIC RECORDING 



479 



variable-density recording and the 100 per cent track level is deter- 
mined by the maximum allowable distortion. 

DISTORTION 

Most of our tests have been made with harmonic-distortion equip- 
ment. Fig. 7 shows the effect of varying the audio level on dis- 
tortion. In this case, distortion is plotted against audio output. 
The optimum bias was used here. 



BIAS CURRENT A- 



500 1000 

FREQUENCY 

Fig. 9 Frequency response. 



(0,000 



Fig. 8 shows curves of distortion versus bias for two audio inputs. 
The two upper curves are output curves and the lower ones are 
corresponding distortion curves. 

FREQUENCY RESPONSE 

Using the optimum bias current and an audio input which is 
safely below the film-overload point for the high frequencies, we ob- 
tain the frequency-response curve of Fig. 9. Since our equipment was 
designed especially for motion picture use, the upper frequency limit 
was set at 8000 cycles. However, we know from experiments that it 
can be held flat to 10,000. The dashed curves show the frequency 



480 O'DEA 

response which would be possible if a lower bias current had been 
used. Had a lower current been used, however, the distortion would 
have gone up. 

NOISE 

In order to make accurate statements concerning signal-to-noise 
ratio for magnetic recording, it is necessary to specify not only the 
maximum harmonic distortion, but also the permissible frequency 
limits and the characteristics of the measuring channel. 

BIBLIOGRAPHY 

(1) "Book of American Society of Testing Materials Standards," Philadelphia 
Pa., 1936. 

(2) J. F. Manildi, "Multiple magnetic circuits," Electronics, pp. 160-163; 
November, 1946. 

(3) Marvin Camras, "Theoretical response from a magnetic-wire record," 
Proc. I.R.E., vol. 34, pp. 597-603; August, 1946. 

(4) W. W. Wetzel, "Review of the present status of magnetic recording 
theory," Audio Eng., pp. 14-17; November, 1947. 

(5) Otto Kornei, "Frequency response of magnetic recording," Electronics, 
pp. 124-128; August, 1947. 

(6) L. C. Holmes and D. L. Clark, "Supersonic bias for magnetic recording," 
Electronics, pp. 126-136; July, 1945. 

(7) D. E. Wooldridge, "Signal and noise levels in magnetic tape recording," 
Trans. A.I.E.E., vol. 65, pp. 342-352; June, 1946. 

(8) Lynn Holmes, "Factors influencing the choice of a medium for magnetic 
recording," J. Acous. Soc. Amer., vol. 19, pp. 395-403; May, 1947. 

(9) R. A. Power, "The German magnetophon," Wireless World, pp. 195-198; 
June, 1946. 

(10) C. N. Hickman, "Sound recording on magnetic tape," Bell Sys. Tech. 
Jour., vol. 16, pp. 165-177; April, 1937. 

(11) James Z. Menard, "High frequency magnetophon magnetic sound re- 
corders," Final Report No. 705, Published by Office of Military Government 
for Germany (U. S.), Office of Director of Intelligence, Field Information Agency, 
Technical, January, 1946. 

(12) Heinz Liibeck, "Magnetic sound recording with film and ringheads" 
(Translated by W. F. Meeker), Akus. Zeits., vol. 2, pp. 273; November, 1937. 

(13) O. W. Eshbach, "Handbook of Engineering Fundamentals," John Wiley 
and Sons, Inc., New York, N. Y., 1936. 

(14) "Magnetic Recording," Reprint from /. Soc. Mot. Pict. Eny., vol. 48, 
pp. 1-62; January, 1947. 



35-Mm Magnetic Recording System* 

BY EARL MASTERSON 

RCA VICTOR DIVISION, CAMDEN, NEW JERSEY 



Summary Ail idea was conceived of designing and building a number of 
kits to add magnetic sound-recording facilities to a standard photographic 
recorder. It is believed that by starting magnetic recording in this manner 
it will enable the studios to obtain some practical experience without the 
expense of a complete film-handling mechanism and yet will not interfere 
with photographic sound-recording production work. The construction of 
the mechanical and electrical components of the kit and the operational 
features are discussed as well as the performance characteristics that can 
be expected of this system. 



i LTHOUGH MAGNETIC RECORDING is one of the oldest recording 
J\. methods known, it was only during the last war that this form of 
recording came into its own. In more recent years the high fidelity 
obtainable by properly designed recording and reproducing equip- 
ment, together with improved recording media, made magnetic re- 
cording actually a competitor in several sound-recording fields. 
Demonstrations of the quality of performance of a laboratory 35-mm 
recorder were given to several groups of Hollywood people in Cam- 
den. New Jersey. It was felt that the quality of reproduction might 
be of great interest to the studios, although it appeared that consider- 
able experience would be necessary to determine how successfully 
this entirely new medium could be fitted into the operations. It 
was also decided that the best method of gaining this experience 
would be to design a conversion kit for a standard photographic sound 
recorder, so that either photographic or magnetic recordings could be 
made on the same machine. In this way operational experience could 
be gained without seriously interfering with regular production work. 
The design and features of a magnetic conversion kit to adapt a well- 
known 35-mm sound recorder for magnetic recording wirl be de- 
scribed. 

Although almost all of the early work in magnetic recording had 
been with solid wire or solid tape, it was found during the war, both 
in this country and especially in Germany, that a better recording 

f* Presented May 18, 1948, at the SMPE Convention in Santa Monica. 

NOVEMBER, 1948 JOURNAL OF THE SMPE VOLUME 51 481 



482 



MASTERSON 



November 



medium could be made in the form of a magnetic coating on a non- 
magnetic support or base such as paper or plastic. This form of mag- 
netic-recording medium shows several advantages over the solid 
type. The two major requirements of a solid recording medium are 
that it be both ductile and a permanent magnet. These requirements 
are not normally compatible. As a result of considerable work on the 
part of wire manufacturers, a satisfactory wire has been developed 
for the average quality requirements of sound recording. One 







Fig. 1 Magnetic conversion kit in PR-23 recorder. 

company has solved the problem of incompatibility by using a brass 
wire which has excellent drawing properties and plating a magnetic 
coating upon this wire which has the proper recording properties. 
This still does not meet the requirements of the strictly high-quality 
sound-recording field. 

By suspending a magnetic oxide in a binder and coating this mix- 
ture on a film-support base, it is possible to combine both the correct 
magnetic qualities and a support having desirable mechanical quali- 
ties. Since the magnetic particles of a coated tape can be extremely 
fine and also well distributed and suspended in a binder, it is possible 






1948 



35-Mn MAGNETIC RECORDING 



483 



to record and reproduce wavelengths of much smaller physical length 
than that possible on solid wire or tape, the factor being something 
like 3 to 1. This means that a magnetic track at the standard 35- 
mm recording speed of 90 feet per minute is capable of producing 
excellent frequency response. 

Hollywood, unlike other sound-recording industries, is quite for- 
tunate in having had years of experience in the handling of long tapes 
or films. This makes the conversion from present recording methods 
to magnetic recording a relatively simple one, so simple, in fact, that a 
conversion kit appears to be a very good answer to the immediate 




Fig. 2 Electrical units of magnetic conversion kit. 

! problem of introducing magnetic recording to Hollywood. In order 
I* to make the kit available to most studios, it was decided that it 
\ should be designed to fit the widely used RCA PR-23 sound recorder. 
Fig. 1 shows the installation of the complete mechanical conversion, 
kit. In applying this kit to the PR-23, a minimum of work is re- 
quired. Several roller studs are pressed out of the frame, and some 
new studs, supplied with the kit, are pressed in, to secure the head and 
idler mounting plate. This conversion mechanism, includes a tight- 
loop sprung idler film filter system and the magnetic-recording and -re- 
producing heads complete with all adjustments. A nonmagnetic 



484 



MASTERSON 



November 



sound drum and shaft is also supplied. Electrical connections for 
the heads are made to small Cannon sockets in the side of the new film- 
compartment housing. 

It is assumed that most users will erase the film as a separate opera- 
tion not connected with recording. However, if it is desired, an 
erasing head can be furnished as a separate kit. This head is pivoted 
on its own mounting plate and rides on the film on the top of the 
sound drum. The sound drum is relieved in the area under the head 
to prevent its bounding or hammering. 




Fig. 3 Film path and magnetic heads. 

Iii order to make the electrical kit as flexible as possible for various 
installation requirements, it was decided to use individual plug-in 
chassis which could be mounted either on a single shelf in a rack or in 
two boxes as shown in Fig. 2. By means of adjustable brackets fur- 
nished with the kit, it is possible to mount these boxes on a wall, on a 
table, or underneath a table. A door is provided in the end of the 
box so that the chassis may be readily removed for servicing. One 
box contains a single chassis which provides an oscillator with its 



1948 



35-Mn MAGNETIC RECORDING 



485 



own power supply for high-frequency bias and erasing currents. 
This chassis also contains the necessary recording equalization cir- 
cuits. A meter on the front panel enables an operator to measure 
bias current. The other box contains two preamplifiers and a chas- 
sis for the playback equalization network. 

Fig. 3 shows the film path with the kit mounted on the PR-23 
recorder. A drawing of the new film path and the mounting arrange- 
ment for the recording and reproducing heads is shown in Fig. 4. 
As the film enters the compartment from the magazine, it passes the 
sprocket in the usual manner and then passes around a sprung idler 
which acts both as a filter and as a film guide for the photographic- 
track placement. After the film passes around the sound drum, it 



KI&W FILM 
COMPARTME-NT 



SPRUNG 
IDLE-R.S 



ERASING 
HE-AD \ 



OPTICAL 

BAR.R.E-L 



SOUND 
DRUM ' 



FILM 




RE-CORDING HEAD -^ / <- RE-PRODUCING HE-AD 

PULL PIN^ 

Fig. 4 Film path showing tight-loop system and mag- 
netic heads in position. 



then goes immediately over the magnetic-recording head and then 
over the magnetic-reproducing head. These heads are arranged on 
movable arms and are linked together. By means of a pull pin, such 
as is sometimes used on pad rollers, it is possible to drop or retract the 
two heads for threading. The heads also remain in the retracted 
position during photographic recordings. The film then passes 
around a fixed idler -and then to a second sprung idler which completes 
the tight-loop filtering system, then around the second side of the 
driving sprocket into the film magazine. The spacing of the record- 
ing and reproducing heads is such that for monitoring purposes the 



486 



MASTERSON 



November 



reproduced signal will lag the actual signal by approximately 1 / 16 of a 
.second. The azimuth of each head is independently adjustable by 
means of a setscrew. By loosening a screw in the center of the head, 
it is possible to rotate head for best contact between gap and film. 

The magnetic-track placement can then be adjusted by means of 
adjusting nuts on the end of the studs around which the head-mount- 
ing arms pivot. Since no standard has been established on the place- 
ment of a magnetic track, it was decided to utilize the equivalent print 
dimensions of the photographic wide-track push-pull system. There- 
fore, the centerline of the magnetic track is identical with that of the 



STANDARD PR.E- AMP 
POW&R SUPPLY . 
AUDIO LINE- 



LINE- FROM 
RE-CORDING | 110 V 

AMP. > 




PR23 

F-ILM R.E-CORDE-R 
WITH MASNE-TlC 
CONVE-RSION K.IT 




RECORDING 



RE-PRODUCING 
MHI 



Fig. 5 Block diagram of electrical units. 

double-width photographic track. The recording-head width is 
184 mils and the reproducing head is 176 mils. In order to maintain 
a balanced support of the film over the two heads, a skid the diameter 
of the head laminations is provided near the back side of the film so 
that the support is symmetrical. Fig. 5 is a block diagram of the 
electrical part of the kit as the units are arranged with the recorder, j 
The line from the recording amplifier which normally plugs into the 
rear of the recorder is now removed and plugged into the rear of the 
recording chassis box. A new cable then goes from this box to the 
recorder to provide connections for photographic recordings. A 
switch is provided on the front of the recording box to select either 



1948 



35-Mn MAGNETIC RECORDING 



487 



photographic or magnetic recording. If it is desired to make 
magnetic recordings, the audio signal is equalized and then mixed 
with the proper amount of high-frequency bias and goes to the re- 
recording head. For playback, either as monitoring or as a film 
phonograph, the output of the playback head is connected to the 
left-hand box by means of another cable and enters the first pre- 
amplifier. The output of this amplifier is then equalized and passes 
to the second preamplifier, the output of which is at mixer level. 
The preamplifiers are powered, and the audio is returned by the stand- 
ard preamplifier connecting cable. 







x 
















N. 














X 














N 














X 


vP 












E 


N 


^^^^ 


*' c 










. 


^ 


A* 








/ 


/A 












/ 








2 




/ 










50 100 500 1000 5000 10.0 



Fig. 6 Response curve of normal system and equalization 
required. 



The solid curve A in Fig. 6 is the uncompensated response of a 
typical magnetic film at 90 feet per minute. If constant current is 
maintained in the recording head at all frequencies, substantially con- 
stant magnetization of the tape will result at all frequencies, but this 
does not mean that a film so recorded will produce a flat response when 
reproduced . Two maj or effects prevent the response from being at all 
flat. The first is that a magnetic-reproducing head is a "rate-of- 
chaiige" device which means that the voltage output is proportional 
to the rate of change of the flux rather than to the amplitude of the 
flux. This effect accounts for the 6-decibel-per-octave rise starting 
at the low-frequency end and, at this film speed, extending up to 



488 MASTERSON 

about 4000 cycles. The second effect which causes the output above 
4000 cycles to fall is due to several factors, one being the in- 
ability of any magnetic material to maintain extremely short, closely 
spaced magnets. This is called self-demagnetization and would, 
perhaps, be equivalent to loss of resolution in a photographic film. 
Another cause of this high-frequency loss is again equivalent to a 
photographic system and that is slit loss or, in this case, gap loss. 
The magnetic gap is and should be smaller than the photographic slit 
and consequently, is of less importance in regard to the high-fre- 
quency loss. A third effect contributing to high-frequency drop is the 
eddy-current loss in the iron in the heads, although this is of minor 
importance, especially if thin laminations of good iron are used. 

It is obvious that considerable equalization will be necessary to 
obtain a flat over-all response, but the uncompensated response is not 
greatly unlike that of an uncompensated disk-record reproducer and 
can be treated in a like manner. It is well known that the energies of 
actual voice and music sounds in the high-frequency range are well 
down in output as compared to their low-frequency output. This 
fact allows a certain amount of high-frequency pre-emphasis. If con- 
stant current in the recording head produces curve A in Fig. 6, and if 
the constant current is obtained by the use of a relatively high resist- 
ance in series with the recording head, it can be seen that a record- 
ing-current curve like curve B in Fig. 6 can be obtained by by-passing 
the constant-current resistor with capacitor of proper size. The 
amount of tip-up or pre-emphasis and how far it is extended is deter- 
mined by the intended frequency response. In this case the specifi- 
cations were for flat response to 8000 cycles. Curve C is then the 
sum of recording pre-emphasis added to the normal playback response. 

Since voice and music energies are at their maximum at low fre- 
quency, it is not possible to use pre-emphasis over this range, so this 
correction must be made during playback. Somewhere in the play- 
back system a characteristic similar to curve D must be inserted. 
Since considerable amplifier gain must be used during playback, this 
equalizer may be used not only to obtain proper response, but also 
to reduce greatly first-tube hiss and noise. This means that this 
equalizer should be used after the first tube or tubes of the playback 
system. In the conversion kit the equalizer is arranged in the circuit 
to follow the first two-stage amplifier. When the response of this 
equalizer is added to the normal response, a flat curve will result, asj 
shown by curve E. 



Optimum High- Frequency Bias 
in Magnetic Recording* 

BY G. L. DIMMICK AND S. W. JOHNSON 

RCA MANUFACTURING COMPANY, CAMDEN, NEW JERSEY 



Summary An experimental study was made of magnetic tapes and 
films produced by several manufacturers. The effects of bias current upon 
the frequency characteristic, the reproducing level, and the harmonic dis- 
tortion are shown. Conclusions are drawn as to the best method of testing 
a given tape for the optimum value of high-frequency bias. 

A HIGH-FREQUENCY BIAS for magnetic recording was first used by 
W. L. Carlson and G. W. Carpenter in 1921. Since that tim